Ferroelectric and Incipient Ferroelectric Properties of a Novel Sr_(9-x)PbxCe2Ti2O36 (x=0-9) Ceramic System
Stanislav Kamba, Maxim Savinov, Frantisek Laufek, Ondrej Tkac, Christelle Kadlec, Sergiy Veljko, Elizabeth J. John, Ganesanpotti Subodh, Mailadil T. Sebastian, … 展开作者
Stanislav Kamba, Maxim Savinov, Frantisek Laufek, Ondrej Tkac, Christelle Kadlec, Sergiy Veljko, Elizabeth J. John, Ganesanpotti Subodh, Mailadil T. Sebastian, Mariana Klementova, Viktor Bovtun, Jan Pokorny, Veronica Goian, Jan Petzelt
Sr_(9-x)PbxCe2Ti12O36 system is derived from the perovskite SrTiO3 and its chemical formula can be written as (Sr_(1-y)Pby)0.75Ce0.167TiO3. We investigated dielectric response of Sr_(9-x)PbxCe2Ti12O36 ceramics (x = 0-9) between 100 Hz and 100 THz at temperatures from 10 to 700 K using low- and high-frequency dielectric, microwave (MW), THz and infrared spectroscopy. We revealed that Sr9Ce2Ti12O36 is an incipient ferroelectric with the R-3c trigonal structure whose relative permittivity e' increases from 167 at 300 K and saturates near 240 below 30 K. The subsequent substitution of Sr by Pb enhances e' to several thousands and induces a ferroelectric phase transition to monoclinic Cc phase for x>=3. Its critical temperature Tc linearly depends on the Pb concentration and reaches 550 K for x=9. The phase transition is of displacive type. The soft mode frequency follows the Barrett formula in samples with x<=2 (typical for quantum paraelectrics) and the Cochran formula for x>=3. The MW dispersion is lacking and quality factor Q is high in samples with low Pb concentration, although the permittivity is very high in some cases. However, due to the lattice softening, the temperature coefficient of the permittivity is rather high. The best MW quality factor was observed for x=1: Q*f=5800 GHz and e'=250. Concluding, the dielectric properties of Sr_(9- x)PbxCe2Ti12O36 are similar to those of Ba_(1-x)SrxTiO3 so that this system can be presumably used as an alternative for MW devices or capacitors.
The consideration of size-induced ferroelectric-paraelectric phase transition for conventional and incipient ferroelectrics thin films with perovskite structure was carried out in phenomenological theory framework of Ginsburg-Landau-Devonshire. The more general form of surface free energy expansion that includes intrinsic surface stress tensor, surface piezoelectric effect and electrostriction as well as quadratic and quartic powers of surface polarization has been considered. The analytical expressions for thickness dependence of transition temperature was derived both for the conventional an…
Cubic structure is one of the most commonly found structures for oxides at high temperature. As the temperature is lowered only a handful of these oxides exhibit ferroelectricity which is rather surprising. In this paper, we use the example of YCrO3 (YCO), an incipient ferroelectric material to show that in most oxides there are two competing phenomenon -onset of ferroelectricity due to rotation of CrO6 octahedra and displacement of Y atom leading to suppression of ferroelectricity. This competition reveals that while the octahedral rotations favor a lower symmetry state, the Y atom displaceme…
A parameterized effective Hamiltonian approach is used to investigate KTaO$_3$. We find that the experimentally observed anomalous dielectric response of this incipient ferroelectric is well reproduced by this approach, once quantum effects are accounted for. Quantum fluctuations suppress the paraelectric--to--ferroelectric phase transition; it is unnecessary to introduce defects to explain the dielectric behavior. The resulting quantum-induced local structure exhibits off-center atomic displacements that display {\sl longitudinal, needle-like correlations} extending a few lattice constants.
The ferroelectric trends of rutile (TiO$_2$) in bulk and at the (110) surface are investigated by means of ab initio density functional theory. We discuss the underlying mechanism of the incipient ferroelectric behavior of rutile in terms of Born effective charges, which we decompose in individual contributions by means of maximally localized Wannier functions. We show that a ferroelectric phase can be stabilized for a variety of different lattice distortions which all enlarge the shortest Ti-O distance, even if the longer apical Ti-O bond is simultaneously shortened. At the (110) surface, the…
Ferroelectrics subject to suitable electric boundary conditions present a steady negative capacitance response. When the ferroelectric is in a heterostructure, this behavior yields a voltage amplification in the other elements, which experience a potential difference larger than the one applied, holding promise for low-power electronics. So far research has focused on verifying this effect and little is known about how to optimize it. Here we describe an electrostatic theory of ferroelectric/dielectric superlattices, convenient model systems, and show the relationship between the negative perm…
Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramics have demonstrated excellent dielectric, ferroelectric and piezoelectric properties in comparison to lead-based materials. The synthesis of pure and crystalline BCZT nanopowders at low temperatures of 25, 80 and 160 C was reported previously by using a sol-gel method followed by a hydrothermal route. In this study, the structural, dielectric and ferroelectric properties of sintered BCZT ceramics at 1250 °C for 10h were investigated. XRD measurements revealed the presence of a single perovskite phase at room temperature with the coexistence of…
The dielectric constant of the incipient ferroelectric EuTiO$_3$ exhibits a sharp decrease at about 5.5K, at which temperature antiferromagnetic ordering of the Eu spins simultaneously appears, indicating coupling between the magnetism and dielectric properties. This may be attributed to the modification of the soft-phonon mode, $T_{1μ}$, which is the main contribution to the large dielectric constant, by the Eu spins(7$μ_B$ per Eu). By adding the coupling term between the magnetic and electrical subsystems as $ -g\sum\limits_l {\sum\limits_{< {i,j}} {q_l^2}} \overrightarrow {S_i} \cdot \overr…
(1-x)Li0.12Na0.88NbO3-xBaTiO3 (0 to x to 0.40) ferroelectric ceramics were prepared using conventional ceramics route and their phase transitional behavior is investigated by using dielectric spectroscopy. The temperature-dependent dielectric permittivity epsilon'(T) shows a diffused ferroelectric-paraelectric transition for all compositions. An acceptable and competent characterizing parameter (D) of diffused phase transition (DPT), defined by Uchino et al. [J Am Ceram Soc 2010;93:4011], was measured and validated. Interestingly, a crossover from diffused ferroelectric phase transition (FE-DP…
SrNaBi2Nb3O12 powder was prepared via the conventional solid-state reaction method. X-ray structural studies confirmed the phase to be a three-layered member of the Aurivillius family of oxides. SrNaBi2Nb3O12 (SNBN) ceramics exhibited the typical characteristics of relaxor ferroelectrics, associated with broad and dispersive dielectric maxima. The variation of temperature of dielectric maxima (Tm) with frequency obeyed the Vogel-Fulcher relationship. Relaxor behavior was believed to be arising from the cationic disorder at A-site. Pinched ferroelectric hysteresis loops were observed well above…
High-mobility layered semiconductors have the potential to enable the next-generation electronics and computing. This paper demonstrates that the ultrahigh electron mobility observed in the layered semiconductor Bi$_2$O$_2$Se originates from an incipient ferroelectric transition that endows the material with a robust protection against mobility degradation by Coulomb scattering. Based on first-principles calculations of electron-phonon interaction and ionized impurity scattering, it is shown that the electron mobility of Bi$_2$O$_2$Se can reach 10$^4$ to 10$^6$ cm$^2$V$^{-1}$s$^{-1}$ over a wi…
Ferroelectric soft mode properties in ceramics and thin films are reviewed and compared with single crystals. In general, the permittivity in ceramics and thin films is markedly reduced compared to the single crystals mainly because of low-permittivity grain boundaries - dead layers - (sometimes also nano-cracks) present in the samples. In SrTiO3 and BaTiO3, this dielectric reduction is fully explained by stiffening of the soft mode frequency. In most other ferroelectrics, the soft mode accounts only partly for such a permittivity reduction, since the transition is only partially driven by the…
We have used a first-principles-based scheme to compute the temperature-versus-misfit strain ``Pertsev'' phase diagram of ultrathin films of {\sl incipient} ferroelectric KTaO$_3$. Our results suggest that, at variance with the bulk material, KTaO$_3$ ultrathin films cannot be described as quantum paraelectrics. Rather, the behavior of the films is largely determined by surface/interface effects that favor ferroelectricity and the imperfect screening of the depolarizing fields. This leads to Pertsev phase diagrams that are qualitatively similar to those of {\sl normal} ferroelectrics such as B…
Dielectric response as a function of frequency for high-permittivity dielectric and ferroelectric materials is discussed emphasizing the dynamic behaviour in the microwave and infrared range. After introducing the usual modelling of the polar phonon response and anharmonic hopping in locally dynamically disordered solids, including discussion of displacive and order-disorder ferroelectric phase transitions, we summarised the experimental data for selected ferroelectric, incipient ferroelectric and antiferroelectric perovskite ceramics (STO, BTO, BST, PZO), discussing the dielectric grain size …
We investigate the low temperature behaviour of Pb(In$_{1/2}$Nb$_{1/2}$)O$_{3}$-Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$-PbTiO$_{3}$ using dielectric permittivity measurements. We compare single crystal plates measured in the [001] and [111] directions with a polycrystalline ceramic of the same composition. Poled crystals behave very differently to unpoled crystals, whereas the dielectric spectrum of the ceramic changes very little on poling. A large, frequency dependent dielectric relaxation seen in the poled [001] crystal around 100 K is much less prominent in the [111] crystal, and doesn't occur in …
Ferroelectric-like hysteresis loops of CaCu3Ti4O12 (CCTO) ceramic have been observed. We found that this unusual feature does not arise from the displacement of the Ti ions in the TiO6 octahedron, but apparently comes from the charges at the grain boundaries which consist of a CuO layer. The relaxation time of 2.9 milliseconds by the charges from the grain boundary, nearly corresponding to the inverse P - V sampling frequency of 1kHz, has been found in the impedance spectrum. According to the micro-Raman mapping, the CuO layer is found in the grain boundary and is perfectly distinguished from …
Many ferroelectric devices are based on doped lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary (MPB), at which the relevant material's properties approach their maximum. Based on a synchrotron x-ray diffraction study of MPB PZT, bulk fatigue is unambiguously found to arise from a less effective field induced tetragonal-to-monoclinic transformation, at which the degradation of the polarization flipping is detected by a less intense and more diffuse anomaly in the atomic displacement parameter of lead. The time dependence of the ferroelectric response…
Observations by in-situ transmission electron microscopy (TEM) reveal the changes in domains morphology in 0.885(Bi1/2Na1/2)TiO3-0.05(Bi1/2K1/2)TiO3-0.015(Bi1/2Li1/2)TiO3-0.05BaTiO3 ceramics. Evolution of the macroscopic ferroelectric domains has been observed at 25 oC to 180 oC. The ferroelectric domains and their walls reduce progressively with increasing temperature. In the selected-area electron diffraction (SAED) patterns the crystallographic evidence of antiferroelectric domain is not found over the temperature range, which provides the evidence that the ferroelectric-antiferroelectric t…
Based on our analytical results [http://arxiv.org/abs/1006.3670], we predict that undoped nanoparticles (size <10-100nm) of incipient ferroelectrics without any magnetic ions can become ferromagnetic even at room temperatures due to the inherent presence of a new type of magnetic defects with spin S=1, namely oxygen vacancies, where the magnetic triplet state is the ground state in the vicinity of the surface (magnetic shell), while the nonmagnetic singlet is the ground state in the bulk material (nonmagnetic core). Consideration of randomly distributed magnetic spins (S=1) had shown that magn…
We report the polarization, displacement current and leakage current behavior of a trivalent nonpolar cation Al cation substituted lead free ferroelectric NBT-BT electroceramics with tetragonal phase and P4mm space group symmetry. Nearly three orders of magnitude decrease in leakage current were observed under electrical poling, which significantly improves microstructure, polarization, and displacement current. Effective poling neutralizes the domain pinning, traps charges at grain boundaries and fills oxygen vacancies with free charge carriers in matrix, thus saturated macroscopic polarizati…
Migration of charged point defects triggered by the local random depolarization field is shown to plausibly explain aging of poled ferroelectric ceramics providing reasonable time and acceptor concentration dependences of the emerging internal bias field. The theory is based on the evaluation of the energy of the local depolarization field caused by mismatch of the polarizations of neighbor grains. The kinetics of charge migration assumes presence of mobile oxygen vacancies in the material due to the intentional or unintentional acceptor doping. Satisfactory agreement of the theory with experi…
Ferroelectric anomalies in most classical ferroelectric materials such as BaTiO3 (BT) and related compounds tend to become diffuse and eventually vanish when the grain size decreases. This has led to question the very existence of ferroelectricity for very small particles. However there are also reports in the literature of ultra-high values of permittivity when specific processes or doping are performed, for instance in the BT-family, or in the CaCu3Ti4O12- family and interpretations using (IBLC) have been proposed. We have considered these effects in the framework of a core-shell model of ce…
A method for evaluating the piezoelectric response of unpoled ferroelectric ceramics from elastic and dielectric measurements is proposed and tested on BaTiO$_3$. The method is based on the observation that the softening in a ferroelectric phase with respect to the paraelectric phase is of piezoelectric origin. The angular averages of the piezoelectric softening in unpoled ceramics are calculated for ferroelectric phases of different symmetries. The expression of the orientational average with the piezoelectric and dielectric constants of single crystal tetragonal BaTiO$_3$ from the literature…
We report here the realization of ferroelectricity, ferromagnetism and magnetocapacitance effect in SrFe12O19 ceramics at room temperature. The ceramics demonstrate a saturated polarization hysteresis loop, two I-V peaks and large anomaly of dielectric constant near Curie temperature. These evidences confirmed the ferroelectricity of SrFe12O19 ceramics after annealing in O2 atmosphere. The remnant polarization of the SrFe12O19 ceramic is 103 μC/cm2. The material also exhibits strong ferromagnetic characterization, the coercive field and remnant magnetic moment are 6192Oe and 35.8emu/g, respect…
Ferroelectric and magnetic properties of Fe-doped K0.45Na0.49Li0.06NbO3 (KNLN) and Cu-doped KNLN ceramics were investigated. Comparing with pure KNLN ceramic, Fe-doped KNLN shows ferromagnetic and ferroelectric properties simultaneously while Cu-doped KNLN shows stronger diamagnetic and ferroelectric properties. The magnetic property in KNLN matrix are believed to be induced by point defects. The ferromagnetism of Fe-doped KNLN can be explained by the F-center exchange mechanism, while the antiferroelectric-like loop and diamagnetism of Cu-doped KNLN was explained by the special defect structu…
A novel lead-free tungsten bronze type ceramic Sr5BiTi3Nb7O30, was prepared by a conventional solid-state reaction route. The room-temperature crystal structure shows an average structure with centro-symmetric space group P4/mbm identified by synchrotron XRD. Temperature dependence of dielectric permittivity indicates that Sr5BiTi3Nb7O30 is a ferroelectric relaxor with Tm near 260 K. The ceramic displays stronger frequency dispersion and lower phase-transition temperature compared with Sr6Ti2Nb8O30. A macroscopic and phenomenological statistical model was employed to describe the temperature d…
Over the past decades, there has been significant interest in new cooling technology based on the electrocaloric effect. The large electrocaloric effect observed in polymeric and inorganic ferroelectric materials made possible development of dielectric cooling devices of a new generation. We report a significant impact of annealing on the electrocaloric effect observed in 12/65/35 PLZT bulk ceramics. The electrocaloric data were obtained by direct measurements. Electrocaloric results confirm the existence of the significant electrocaloric response in this relaxor ferroelectric PLZT composition…
Local structural symmetries play a key role in the functionalities of ferroelectric materials and are often found different from average symmetry. Here, we study the real space nanoscale structure in Pb-free BaZr$_{x}$Ti$_{1-x}$O$_{3}$ (x $\leq$ 0.10) by pair distribution function measurements, complemented by transmission electron microscopy and x-ray diffraction. Our observations show existence of the rhombohedrally distorted unit cells; however, at intermediate length scales, at least up to 5 nm, there exist nano-scale correlated regions of monoclinic symmetry. This is complemented by the o…
Microstrctural, vibrational, ferroelectric and dielectric properties investigation reveals non-stoichiometric chemical ordered regions (CORs) and relaxor like dielectric characteristics in lead magnesium niobate (PMN) ceramics uniaxially hot pressed (HP) at 800 oC to 1200 oC. Occurance of (1/2 1/2 1/2) superlattice reflections along <111> in <110> zone axis SAED pattern as well as the presence of bright nano-meter regions in corresponding dark-field images in 800 oC hot pressed PMN demonstrates formation of the CORs as soon as perovskite phase is formed during calcination and remains unaffecte…
We performed factor-group analysis of all phonons in possible monoclinic C2/c and C2 structures of BiMnO3 and compared it with our experimental infrared and Raman spectra. We conclude that the crystal structure is centrosymmetric C2/c in the whole investigated temperature range from 10 to 550 K, therefore BiMnO3 cannot be ferroelectric. We revealed a dielectric relaxation in THz spectra above the structural phase transition taking place at T_C1=475 K giving evidence in strong lattice anharmonicity and a large dynamical disorder of Bi cations above T_C1. Step-like dielectric anomaly observed at…
The importance of a high shear coefficient d15 (or d24) to the piezoelectric properties of domain-engineered and polycrystalline ferroelectrics is discussed. The extent of polarization rotation, as a mechanism of piezoelectric response, is directly correlated to the shear coefficient. The terms "rotator" and "extender" are introduced to distinguish the contrasting behaviors of crystals such as 4mm BaTiO3 and PbTiO3. In "rotator" ferroelectrics, where d15 is high relative to the longitudinal coefficient d33, polarization rotation is the dominant mechanism of piezoelectric response; the maximum …
The thermal conductivity of polycrystalline bulk PZT (lead-zirconate-titanate) has been investigated according to electrical boundary conditions and poling. The thermal conductivity of poled PZT was measured in the poling direction for open circuit and short circuit conditions. The short circuit thermal conductivity had the largest thermal conductivity. The relationship between these two thermal properties, the electrothermal coupling factor $k_{33}^κ$, was found to be similar to the electromechanical coupling factor $k_{33}$ relating elastic compliance under short circuit and open circuit con…
The electrocaloric (EC) effect and energy storage properties of eco-friendly ferroelectric Ba0.9Sr0.1Ti1-xSnxO3 (BSTS-x) ceramics prepared by the conventional solid-state reaction method were studied. Significant energy efficiency exceeding 80% was found in our samples. In particular, BSTS-5 and BSTS-10 samples exhibit 92% and 88% efficiency, respectively, over a wide temperature range around room temperature (RT). Direct EC measurement and an indirect method based on the thermodynamic approach were used to characterize the EC effect, and both yielded consistent results. The largest electrocal…
The combination of antiferroelectricity (AFE) and ferromagnetism (FM) in one structure would allow the development of new type of multiferroic candidates, which be applicable not only in magnetoelectric memories but also in novel energy storage devices. Here we propose a novel type of multiferroic candidate LaxSr1-xFe12O19, whose room temperature state could betuned from ferroelectrics (FE) to antiferroelectrics by changing x from 0 to 0.5. The emphasis of this paper will be focused on the La0.5Sr0.5Fe12O19 system, in which full AFE and FM coexist. The pure antiferroelectric behavior in La0.5S…
The dielectric properties of tantalum doped BaTi0.85Zr0.15O3 were investigated. The conventional solid state reaction method was used to make the ceramic samples. The composition was close to the pinch point of the three structure phase transitions in BaTiO3. Powder X-ray diffraction result indicated that the samples were in very slightly distorted rhombohedral structure at room temperature, and the dielectric measurement showed only cubic-to-rhombohedral phase transition occurred. Instead of a sharp peak characteristic of a ferroelectric (FE) transition, the large dielectric response was simi…
PbTiO3 has the highest tetragonal distortion (c/a=1.064) and highest spontaneous polarization among perovskite titanates. But, it is hazardous and hence one needs to reduce Pb content by substituting or reducing Pb content for use in applications. Pb(1-x)(K0.5Sm0.5)xTiO3 (0&x&0.5) perovskite powders were synthesized by sol-gel process, where Pb2+ was replaced by a combination of K+10.5Sm+30.5 (equivalent charge and comparable ionic radius) providing an excellent substitution model to study changes in structural and electrical properties. Vibrational properties and dielectric properties are mod…
Based on the two-step-switching model, the process of electromechanical poling of a ferroelectric ceramics is simulated. A difference of the remnant polarizations between two poling protocols (mechanical stress is applied before and after the application of poling field) is found from our simulations, which is also observed in experiment. An explanation is given to illustrate why the remnant polarization for the case that mechanical stress is loaded after the application of electric field is larger than the case that mechanical stress is loaded before the application of electric field. Our sim…
It is demonstrated based on continuum mechanics modeling and simulation that it is possible to obtain polycrystalline ceramic ferroelectric materials which beggars single crystals in electromechanical properties. The local inhomogeneities at the ferroelectric domain-scale level due to spontaneous polarization and the underlying anisotropy are taken into consideration in the framework of mathematical homogenization of physical properties in ferroelectric materials. The intrinsic randomness of the spatial distribution of polarization is shown to be judiciously employed for the design of better p…
We show that the type-II multiferroic properties of bulk MnWO4 are kept in nanostructured ceramics of 50 nm grain size prepared via spark plasma sintering (SPS). This means that ferroelectric polarization is robust against downsizing, which is at variance with standard ferroelectrics like BaTiO3. We ascribe this stability to the spin-driven nature of the ferroe-lectric correlations in type-II multiferroics while it is resulting from lattice distortion in other cases. This may open the way for persistent type-II multiferroicity with no need for external stabilization like substrate-generated st…
Environmentally benign (1-x)Ba(Ti$_{0.8}$Zr$_{0.2}$)O$_3$-x(Ba$_{0.7}$Ca$_{0.3}$)TiO$_3$ (BZT-BCT) ceramics are promising materials due to their remarkable high piezoresponse [Liu and Ren, Phys. Rev. Lett. \textbf{103}, 257602 (2009)]. In this Letter, by focusing on local and average structure in combination with macroscopic electromechanical and dielectric measurements we demonstrate the structure property relationship in the tetragonal BZT-BCT ceramic. During high-temperature cubic to tetragonal phase transformation, polar nanoregions are manifested through the spontaneous volume ferroelectr…
Dielectric response e*(f,T) and polar phonon spectra of coarse grain (grain size ~ 4 mkm) and fine grain (grain size ~ 150 nm) ceramics of PbMg_(1/3)Nb_(2/3)O3-35%PbTiO3 were investigated at temperatures 10 - 900 K. e*(f,T) in coarse-grain ceramics exhibits relaxor behavior at high temperatures and a sharp anomaly at the ferroelectric phase transition. The fine-grain ceramics exhibit mainly relaxor ferroelectric behavior with a smaller dielectric constant. The difference is explained by different relaxational dynamics of polar nanoclusters, which appear to be more stabilized at high temperatur…
Polymer-piezoceramic 0-3 composites combine the flexibility of the polymers and the excellent piezoelectric properties of the ferroelectric based ceramic. While grain size of the ceramic powder is one of the important considerations in the fabrication of such composites, a correlation relating poling field induced structural changes and its possible influence on the overall piezoelectric response of the composite is still lacking. In this paper, we examine this issue on a 0-3 piezo-composite comprising of a ceramic powders of a low-lead piezoelectric alloy (x)Bi(Ni1/2Zr1/2O3-(1-x)PbTiO3 in pro…
The structural phase transition in hexagonal BaMnO$_3$ occurring at $T_c$=130 K was studied in ceramic samples using electron and X-ray diffraction, second harmonic generation as well as by dielectric and lattice dynamic spectroscopies. The low-temperature phase (space group $P6_{3}cm$) is ferroelectric with a triplicated unit cell. The phase transition is driven by an optical soft mode from the Brillouin-zone boundary [$q = (\frac{1}{3},\frac{1}{3},0)$]; this mode activates in infrared and Raman spectra below $T_c$ and it hardens according to the Cochran law. Upon cooling below $T_c$, the per…
Phase, microstructural, dielectric and ferroelectric properties investigation clearly reveal that the charge imbalance created due to alio-valent Gd3+-ion substitution at Pb2+ site in lead magnesium niobate should be compensated by changing B-site cation ratio instead of creating A-site or B-site vacancies. Microstructure analysis along with elemental mapping exhibit segregation of magnesium oxide (MgO) and gadolinium niobate (GdNbO4) phase, which is observed to remain invariant to the charge compensation mechanism. Fitting of frequency dependent temperature of dielectric constant maximum Tm (…
We report magnetization measurements and magnetic resonance data for SrTiO3 doped by manganese. We show that the recently reported coexistent spin and dipole glass (multiglass) behaviours are strongly affected by the distribution of Mn ions between the Sr and Ti sites. Motivated by this finding we calculate the magnetic interactions between Mn impurities of different kinds. Both LSDA+U and many-body perturbation theory evidence that magnetic and magnetoelectric interactions are mediated by Mn$_B^{4+}$ ions substituting for Ti. We propose two microscopic magnetoelectric coupling mechanisms, whi…
Simultaneous occurrence of big ferroelectricity and strong ferromagnetism has been observed in Barium Hexaferrite ceramics. Barium hexaferrite (BaFe12O19) powders with hexagonal crystal structure have been successfully synthesized by polymer precursor method using barium acetate and ferric acetylacetonate as the precursor. The powders were pressed into pellets, which were sintered into ceramics at 1100^{\circ}C~1300^{\circ}C for 1 hour. The structure and morphology have been determined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Large spontaneous polariz…
An optimization procedure determining the ideal configuration at the microstructural level of ferroelectric (FE) materials is applied to maximize piezoelectricity. Piezoelectricity in ceramic FEs differ significantly from that of single crystals because of the presence of crystallites (grains) possessing crystallographic axes aligned imperfectly. The piezoelectric properties of a polycrystalline (ceramic) FE is inextricably related to the grain orientation distribution (texture). The set of combination of variables, known as solution space, which dictates the texture of a ceramic is unlimited …
Structural, impedance, ferroelectric and magnetic properties were examined in multiferroic Bi_{2}Fe_{4(1-x)}Co_{4x}O_{9} (0$\leq$x$\leq$0.02) ceramics synthesized via solid-state reaction method. X-ray diffraction analysis and Rietveld refinement showed secondary phase formation (for x$\geq$0.01) which was subsequently confirmed from room temperature Raman spectroscopy study. The frequency dependence of impedance and electric modulus of the material showed the presence of non-Debye type relaxation in all the samples. The values of the activation energies calculated from imaginary impedance and…
A series of Pb-free ferroelectric materials Ba0.9Sr0.1Ti1-xSnxO3 (BSTS-x) with 0 < x < 0.15 was successfully prepared via solid-state reaction method. The effect of Sn substitution on the crystal structure, microstructure, dielectric behavior, ferroelectric and tunable features of BSTS-x ceramics were systematically investigated. Room temperature (RT) x-ray diffraction (XRD) analysis using the Rietveld refinement method reveals that all the synthesized BSTS-x ceramics were well crystallized into single perovskite structure. The results show a tetragonal phase for 0.00 < x < 0.02, which evolves…
Piezoelectric and ferroelectric ceramics with a high Curie temperature (Tc) have attracted a growing attention owning to their applications under severe environments. In this work, phase structure, dielectric, ferroelectric and piezoelectric properties of (0.975-x)BiScO3-xPbTiO3-0.025Pb(Cd1/3Nb2/3)O3 ceramics (x = 0.58-0.64) were studied. A composition-induced structural transformation occurs from rhombohedral phase to tetragonal phase through an intermediate monoclinic phase with the increasing PT concentration. The relationship between structure and electrical properties of the system were d…
Dielectric measurements on 0.65[Pb(Ni_1/3Nb_2/3)O_3]-0.35PbTiO_3 ceramic in the temperature range 90K to 470K shows a relaxor ferroelectric transition around 350K with a Vogel-Fulcher freezing temperature of 338K and appearance of a non-ergodic relaxor ferroelectric phase of tetragonal structure at room temperature. This non-ergodic phase reenters into the relaxor state at low temperatures as evidenced by the appearance of a frequency dependent anomaly in the imaginary part of the dielectric constant around 160K, similar to those reported in other relaxor ferroelectric based morphotropic phase…
The intrinsic ferroelectricity and related dielectric properties of M-type Barium Hexaferrite (BaFe12O19) with excellent magnetic performance are reported in this paper. A classic electric polarization (P-E) hysteresis loop with full saturation, together with two nonlinear reversal current peaks in the I-V curve and huge change of dielectric constant in the vicinity of Curie temperature, have all demonstrated themselves as sufficient experimental evidences to verify the ferroelectricity of BaFe12O19 ceramics. It holds a large remnant polarization at 108 uC/cm2 and a suitable coercive field at …
The dielectric and structural order-disorder properties of as-sintered complex perovskite (x)Pb(In1/2Nb1/2)O3:(1-x)Pb(Mg1/3Nb2/3)O3 ceramics are highly influenced by the quantity of Pb(In1/2Nb1/2)O3 (PIN). High PIN quantity causes the relative permittivity maxima to decrease and the temperature (Tmax) to increase. Also, strong frequency dispersion is dominant in the relative permittivity plotted against the temperature. In the ferroelectric hysteresis loop measurements, the maximum values of electric displacements (Dmax) decrease with increasing PIN. The ceramics in the composition range x = 0…
Ba{[Gax,Tax]Ti(1-2x)}O3 ceramics with x equal to 0, 0.0025, 0.005, 0.01, 0.025 and 0.05 have been prepared by conventional solid-state reaction. Structural and dielectric characterization have been performed to investigate the effect of dipole-pair substitution concentration on the macroscopic dielectric properties. Ba{[Gax,Tax]Ti(1-2x)}O3 evolves from a classic ferroelectric to a diffuse phase transition (DPT) as x increases. Ba{[Gax,Tax]Ti(1-2x)}O3 for x > or = 0.01 possesses diffuseness parameters comparable to Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) and recently reported (Ba0.97Pr0.03)(Ti0.9425Ce…
The structural, dielectric and ferroelectric properties of lead-free (Na0.5-xKxBi0.5-xLax)TiO3 powders synthesized by sol-gel self-combustion method were investigated. Rietveld refinement of Synchrotron x-ray diffraction data confirms pure single phase rhombohedral crystal structure with R3c space group for all the compositions and anti-phase octahedral tilting angle decreased with increase in composition x. Homogeneity and elemental proportions were confirmed by Energy dispersive x-ray spectrometry. The temperature-dependent dielectric study has shown two diffuse type of dielectric anomaly fo…
Recent findings of a large electrocaloric (EC) effect in polymeric and inorganic ferroelectric materials open a potential possibility of development of solid-state cooling or heating devices of new generation with better energy efficiency that may be less harmful for the environment. We investigate by using direct measurements, the temperature and electric field dependence of the electrocaloric response in Pb1-xLax(ZryTi1-y)1-x/4O3 bulk ceramics (PLZT) with x=0.06 and 0.12. Here, the properties of the EC response were probed in a part of the PLZT composition phase diagram with low y=0.40 compo…
Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramic exhibits excellent dielectric, ferroelectric and piezoelectric properties at the Morphotropic Phase Boundary (MPB). Previously, we demonstrated that the use of the anionic surfactant Sodium Dodecyl Sulfate (SDS, NaC12H25SO4) could enhance the dielectric properties of BCZT ceramic using surfactant-assisted solvothermal processing [1]. In the present study, structural, dielectric, ferroelectric properties, as well as electrocaloric effect and energy storage performances of this BCZT ceramic were thoroughly investigated. X-ray diffraction (XRD) …
