We formulate an effective model for B-B' site ordering in double perovskite materials A_2BB'O_6. Even within the simple framework of lattice-gas type models, we are able to address several experimentally observed issues including nonmonotonic dependence of the degree of order on annealing temperature, and the rapid decrease of order upon overdoping with either B or B' species. We also study ordering in the `ternary' compounds A_2BB'_{1-y}B''_yO_6 Although our emphasis is on the double perovskites, our results are easily generalizable to a wide variety of binary and ternary alloys.
Recently an antiferromagnetic metal phase has been proposed in double perovskites materials like Sr$_{2}$FeMoO$_{6}$ (SFMO), when electron doped. This material has been found to change from half-metallic ferromagnet to antiferromagnetic metal (AFM) upon La-overdoping. The original proposition of such an AFM phase was made for clean samples, but the experimental realization of La-overdoped SFMO has been found to contain a substantial fraction of antisite defects. A phase segregation into alternate Fe and Mo rich regions was observed. In this paper we propose a possible scenario in which this ty…
Combining experimental investigations and first-principles DFT calculations, we report physical and magnetic properties of Gd-substituted Y$_2$CoMnO$_6$ double perovskite, which are strongly influenced by antisite-disorder-driven spin configurations. On Gd doping, Co and Mn ions are present in mixed-valence (Co$^{3+}$, Co$^{2+}$, Mn$^{3+}$ and Mn$^{4+}$) states. Multiple magnetic transitions have been observed: i) paramagnetic to ferromagnetic transition is found to occur at \textit{T}$_C$=95.5 K, ii) antiferromagnetic transition at \textit{T}$_N$=47 K is driven by $3d-4f$ polarisation and ant…
Lattice defects affect the long-term stability of halide perovskite solar cells. Whereas simple point defects, i.e., atomic interstitials and vacancies, have been studied in great detail, here we focus on compound defects that are more likely to form under crystal growth conditions, such as compound vacancies or interstitials, and antisites. We identify the most prominent defects in the archetype inorganic perovskite CsPbI$_3$, through first-principles density functional theory (DFT) calculations. We find that under equilibrium conditions at room temperature, the antisite of Pb substituting Cs…
The predicted physical properties of double perovskites have usually been compromised by their intrinsic B-antisite (AS) disorder effect, but the relationship between them is still unclear for the La2MnCoO6 (LMCO) system. This study focuses on controlling the AS disorder and quantitatively reveals correlations with magnetic and electronic states in epitaxial LMCO films grown on (111) SrTiO3 substrates. The AS fraction was precisely controlled by tuning the growth conditions as evaluated from saturation magnetization and x-ray reflection profiles. The saturation magnetization at 5 K decreased l…
Doping at the rare-earth site by divalent alkaline-earth ions in perovskite lattice has witnessed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degrees of freedom. Here, we report an antisite disorder driven spontaneous exchange bias effect as a result of hole carrier (Sr2+) doping in La2-xSrxCoMnO6 (0 < x < 1) double perovskites. X-ray diffraction and Raman spectroscopy have evidenced an increase in disorder with the increase of Sr content up to x = 0.5 and thereby decreases from x = 0.5 to 1. X-ray absorption spectroscopy has revealed that onl…
Double perovskite, (Sr1-xNdx)2FeMoO6, was doped with electrons through partial substitution of divalent Sr by trivalent Nd (0 < x < 0.2). The Fe valence and the degree of B-site order were probed by 57Fe Mossbauer spectroscopy. Replacing Sr by Nd increased the fraction of Fe and Mo atoms occupying wrong sites, i.e. antisite disorder. It had very little effect on the Fe valence: a small but visible increase in the isomer shift was seen for the mixed-valent FeII/III atoms occupying the right site indicating a slight movement towards divalency of these atoms, which was more than counterbalanced b…
Single-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO3, a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density…
We report on atomic ordering of B-site transition-metals and magnetic properties of epitaxial La2CrFeO6 double-perovskite films grown by pulsed-laser deposition under various conditions. The highest ordered sample exhibited a fraction of antisite-disorder of only 0.05 and a saturation magnetization of ~2μ_{B} per formula unit at 5 K. The result is consistent with the antiferromagnetic ordering of local spin moment (3d^{3}_{\downarrow}3d^{5}_{\uparrow}; S = -3/2+5/2 = 1). Therefore, the magnetic ground state of La2CrFeO6 double-perovskite that has been long debate is unambiguously revealed to b…
We investigated the Li+ ion incorporation in Ba2GdNbO6:Eu3+ perovskite by atomistic simulations based on energy minimization. We predicted the most probable sites occupied by Eu3+ and Li+ ions and the related charge-compensation mechanisms involved into these substitutions. The results show that the Eu3+ and Li+ ions are incorporated mainly at the Gd3+ site. In the Li+ ion case, there is a charge compensation by Nb_Gd antisite. The Crystal field parameters and the transition levels for the Eu3+ ion in the BGN:Eu3+ were calculated with basis on the simulated local symmetry of the Eu3+ site. The…
Weak antiferromagnetic (AF) interaction in the ferromagnetic (FM) partially ordered La2CoMnO6 (LCMO) was detected by Raman spectroscopy by monitoring spin-phonon coupling. Because of the sensibility to probe short-range disorder and lattice modifications, the Raman spectroscopy showed to be an useful tool to indicate less remarkable magnetic transitions in LCMO compound. Apart from the expected spin-phonon coupling due to the long-range FM superexchange (Tc~230 K), phonons parameters pointed out an additional spin-phonon coupling related to the short-range AF interaction at Tc~135 K, which was…
We present a simple ionic model which successfully reproduces the various types of compositional long-range order observed in a large class of complex insulating perovskite alloys. The model assumes that the driving mechanism responsible for the ordering is simply the electrostatic interaction between the different ionic species. A possible new explanation for the anomalous long-range order observed in some Pb relaxor alloys, involving the proposed existence of a small amount of Pb^4+ on the B sublattice, is suggested by an analysis of the model.
Engineering oxygen octahedra rotation patterns in $ABO_3$ perovskites is a powerful route to design functional materials. Here we propose a strategy that exploits point defects that create local electric dipoles and couple to the oxygen sublattice, enabling direct actuation on the rotational degrees of freedom. This approach, which relies on substituting an $A$ site with a smaller ion, paves a way to couple dynamically octahedra rotations to external electric fields. A common antisite defect, $\mathrm{Al_{La}}$ in rhombohedral LaAlO$_3$ is taken as a prototype to validate the idea, with atomis…
We have studied the atomic ordering of B-site transition metals and magnetic properties in the pulsed-laser deposited films of La2CrFeO6 (LCFO) and La2VMnO6 (LVMO), whose bulk materials are known to be single perovskites with random distribution of the B-site cations. Despite similar ionic characters of constituent transition metals in each compound, the maximum B-site order attained was surprisingly high, ~90% for LCFO and ~80% for LVMO, suggesting a significant role of epitaxial stabilization in the spontaneous ordering process. Magnetization and valence state characterizations revealed that…
We investigate the structure--property relationships in $AB$O$_3$ perovskites exhibiting octahedral rotations and cooperative octahedral breathing distortions (CBD) using group theoretical methods. Rotations of octahedra are ubiquitous in the perovskite family, while the appearance of breathing distortions -- oxygen displacement patterns that lead to approximately uniform dilation and contraction of the $B$O$_6$ octahedra -- are rarer in compositions with a single, chemically unique $B$-site. The presence of a CBD relies on electronic instabilities of the $B$-site cations, either orbital degen…
We use first-principles density functional theory-based calculations to investigate structural instabilities in the high symmetry cubic perovskite structure of rare-earth (R $=$ La, Y, Lu) and Bi-based biferroic chromites, focusing on $Γ$ and $R$ point phonons of states with para-, ferro-, and antiferromagnetic ordering. We find that (a) the structure with G-type antiferromagnetic ordering is most stable, (b) the most dominant structural instabilities in these oxides are the ones associated with rotations of oxygen octahedra, and (c) structural instabilities involving changes in Cr-O-Cr bond a…
With high-resolution photoemission spectroscopy measurements, the density of states (DOS) near the Fermi level ($E_\mathrm{F}$) of double perovskite Sr$_2$FeMoO$_6$ having different degrees of Fe/Mo antisite disorder has been investigated with varying temperature. The DOS near $E_\mathrm{F}$ showed a systematic depletion with increasing degree of disorder, and recovered with increasing temperature. Altshuler-Aronov (AA) theory of disordered metals well explains the dependences of the experimental results. Scaling analysis of the spectra provides experimental indication for the functional form …
This work investigates the origins of cation ordering of double perovskites using first-principles theory computations combined with machine learning (ML) and causal relations. We have considered various oxidation states of A, A', B, and B' from the family of transition metal ions to construct a diverse compositional space. A conventional framework employing traditional ML classification algorithms such as Random Forest (RF) coupled with appropriate features including geometry-driven and key structural modes leads to highly accurate prediction (~98%) of A-site cation ordering. We have evaluate…
The electronic and magnetic properties of monoclinic double perovskite Sr$_2$CeIrO$_6$ were examined based on both experiments and first-principles density functional theory calculations. From the calculations we conclude that low-spin-state Ir$^{4+}$ (5$\textit{d}^5$, S=$\frac{1}{2}$) shows t$_{2g}$ band derived anti-ferro type orbital ordering implying alternating occupations of $\textit{d}_{yz}$ and $\textit{d}_{xz}$ orbitals at the two symmetrically independent Ir sites. The experimentally determined Jahn-Teller type distorted monoclinic structure is consistent with the proposed orbital or…
We successfully dope the magnetically silent double perovskite semiconductor Sr2GaSbO6 to induce ferromagnetism and tune its band gap, with Ga3+ partially substituted by the magnetic trivalent cation Mn3+, in a rigid cation ordering with Sb5+. Our new ferromagnetic semiconducting Sr2Ga1-xMnxSbO6 double perovskite, which crystallizes in tetragonal symmetry (space group I4/m) and has tunable ferromagnetic ordering temperature and band gap, suggests that magnetic ion doping of double perovskites is a productive avenue towards obtaining materials for application in next-generation oxide-based spin…
We consider magnetic ordering in materials with negative charge transfer energy, such as iron perovskite oxides. We show that for a large weight of oxygen holes in conduction bands, the double exchange mechanism favors a helicoidal rather than ferromagnetic spin ordering both in metals, e.g. SrFeO_3 and insulators with a small gap, e.g. CaFeO_3. We discuss the magnetic excitation spectrum and effects of pressure on magnetic ordering in these materials.
We analyzed the possible magnetic and orbital orderings of double perovskites, using a simple extension of the double exchange model well suited for these compounds. Orbital ordering is favored by the on site repulsion at the Fe ions. We obtain a rich phase diagram, including ferri- and antiferromagnetic phases, which can, in turn, be metallic or insulating, depending on the existence of orbital order.
Ambiguity in B-Site cation ordering: A Case study of the double perovskite Ca$_2$CoNbO$_6$
Skolkovo Institute of Science and Technology（斯科尔科沃科学技术研究所）；Zavoisky Physical-Technical Institute, Federal Research Center “Kazan Scientific Center of RAS”（扎沃伊斯基物理技术研究所，俄罗斯科学院鞑靼斯坦科学中心联邦研究中心）；Kazan (Volga Region) Federal University（喀山（伏尔加沿岸）联邦大学）；Institute of Solid State Chemistry of the Russian Academy of Sciences (UB)（俄罗斯科学院固体化学研究所（乌拉伯分支））
The atomic ordering in complex perovskite alloys is investigated by the cluster variation method (CVM). For the 1/3\{111\}-type ordered structure, the order-disorder phase transition is the first order, and the order parameter of the 1:2 complex perovskite reaches its maximum near x=0.25. For the 1/2\{111\}-type ordered structure, the ordering transition is the second order. Phase diagrams for both ordered structures are obtained. The order-disorder line obeys the linear law.
Electron- and hole-doped La$_2$CoMnO$_6$(LCMO) are investigated using first principles DFT calculations. Hole and electron doping are achieved respectively by introducing Sr$^{2+}$ at La$^{3+}$ sites and by inducing O-site vacancies in LCMO. Electronic structure calculations suggest that hole doping alters the charge and valence state of Co ions, whereas electron doping influences the Mn ions. Introduction of defects is found to enhance antisite disorder(ASD) at Co/Mn site, which is expected to influence the magnetodielectric properties of the system. Our calculations suggest that while ASD an…
The synthesis and structural study of the stoichiometric perovskite La0.5Ba0.5CoO3 have allowed three forms to be isolated. Besides the disordered La0.5Ba0.5CoO3 and the perfectly ordered layered LaBaCo2O6, a third form called nanoscale-ordered LaBaCo2O6, is obtained. As evidenced by transmission electron microscopy investigations, the latter consists of 112-type 90 degree oriented domains fitted into each other at a nanometer scale which induce large strains and consequently local atomic scale lattice distortions. These three ferromagnetic perovskites exhibit practically the same Tc (174-179 …
In this work we investigated the phase formation and structural ordering of Ba$_{3}$B$^{'}$Nb$_{2}$O$_{9}$ (B$^{'}$ $=$ Ca and Zn) perovskite powders obtained by a modified polymeric precursor route using X-ray powder diffraction and Raman spectroscopy. We obtained single phase complex perovskites at 900 $^o$C. Williamson-Hall analysis and scanning electron microscopy showed that the powders have crystallites and particles of nanometric size.
In this work we performed a detailed investigation about ordering in \bcn perovskite. The sintering temperature and time were changed to obtain samples with different ordering. The order parameters were probed by Raman spectroscopy based on a partial disordered model. To use the partial disordered model correctly we performed {\it ab initio} calculations in \bcn to assign the optical phonons. The results showed that sintering temperature improves order while sintering time is not so efficient to promote order.
Rare earth based cobalt-ruthenium double perovskites A$_2$CoRuO$_6$ (A = La, Pr, Nd and Sm) were synthesized and investigated for their structural and magnetic properties. All the compounds crystallize in the monoclinic $P2_1/n$ structure with the indication of antisite disorder between Co and Ru sites. While, La compound is already reported to have an antiferromagnetic state below 27 K, the Pr, Nd and Sm systems are found to be ferrimagnetic below $T_c$ = 46, 55 and 78 K respectively. Field dependent magnetization data indicate prominent hysteresis loop below $T_c$ in the samples containing m…
Cation ordering is most common process detected in A$_{3}$B'B"$_{2}$O$_{9}$-based complex perovskites. Some important physical features of this system are due to the B-site ordering at long and short range. For microwave applications as filters and resonators, the 1:2 order is more appropriate. Otherwise, the oxygen vacancies and 1:1 order are considered the main factors behind the good performance of nonstoichiometric A$_{3}$B'$_{1+x}$B"$_{2-x}$O$_{9-δ}$-based ceramics as proton conductors. Until now, however, there are no available reports regarding the isolated effects of B-site order at lo…
The effective Hamiltonian for perovskite titanates is derived by taking into account the three-fold degeneracy of $t_{2g}$ orbitals and the strong electron-electron interactions. The magnetic and orbital ordered phases are studied in the mean-field approximation applied to the effective Hamiltonian. A large degeneracy of the orbital states in the ferromagnetic phase is found in contrast to the case of the doubly degenerate $e_g$ orbitals. Lifting of this orbital degeneracy due to lattice distortions and spin-orbit coupling is examined. A general form for the scattering cross section of the res…
Based on density functional theory, the electronic and optical properties of hybrid organic/perovskite crystals are thoroughly investigated. We consider the mono-crystalline 4FPEPI as material model and demonstrate the optical process is governed by three active Bloch states at the Γ point of the reduced Brillouin zone with a reverse ordering compared to tetrahedrally bonded semiconductors. Giant spin-orbit coupling effects and optical activities are subsequently inferred from symmetry analysis.
In this work, we use density functional theory calculations to demonstrate how spontaneous electric polarizations can be induced \textit{via} a hybrid improper ferroelectric mechanism in iodide perovskites, a family well-known to display solar-optimal band gaps, to create new materials for photoferroic applications. We first assemble three chemically distinct ($A$$A^{\prime}$)($B$$B^{\prime}$)I$_6$ double perovskites using centrosymmetric $AB$I$_3$ perovskite iodides (where $A$ = Cs, Rb, K and $B$ = Sn, Ge) as building units. In each superlattice, we investigate the effects of three types of $…
The oxygen-exchange behavior has been studied in half-doped manganese and cobalt perovskite oxides. We have found that the oxygen diffusivity in Gd_{0.5}Ba_{0.5}MnO_{3-δ} can be enhanced by orders of magnitude by inducing crystallographic ordering among lanthanide and alkali-earth ions in the A-site sublattice. Transformation of a simple cubic perovskite, with randomly occupied A-sites, into a layered crystal GdBaMn_2O_{5+x} (or isostructural GdBaCo_2O_{5+x} for cobalt oxide) with alternating lanthanide and alkali-earth planes reduces the oxygen bonding strength and provides disorder-free chan…
We report the understanding of the electronic band structure of $Cs_4CuSb_2Cl_{12}$ perovskite through first-principles density-functional theory calculations. We find that the most stable state has the antiferromagnetic configuration where each $[CuCl_6]$ octahedral chain along the [010] direction is antiferromagnetic. The reasonable band structure of the compound can be obtained only if both the correct magnetic order and the improved exchange interaction of the Cu $\it{d}$ electrons are taken into account.
Ordered double perovskite oxides of the general formula, A2BB'O6, have been known for several decades to have interesting electronic and magnetic properties. However, a recent report of a spectacular negative magnetoresistance effect in a specific member of this family, namely Sr2FeMoO6, has brought this class of compounds under intense scrutiny. In this small review, we present few theoretical and experimental results, describing mainly the effects of Fe/Mo antisite defects on the properties of this compound and also briefly discuss few other puzzling facts about this fascinating compound
Dielectric study on Ca3Mn2O7 features relaxor-like segmented dynamics below the antiferromagnetic ordering. Dipolar relaxations of different origin are spectrally resolved exhibiting distinct H-field alterations. This identifies their allegiance to different magnetic sub-phases and establishes dual coupling of electrical, magnetic, and structural degrees of freedom. Further, strong spin-lattice coupling has been affirmed with Raman spectroscopy across the magnetic ordering. Short-range electrical correlations collaterally cause measurable harmonic dielectric response in the system. The \c{hi}_…
Charge-lattice fluctuations are observed in the layered perovskite manganite LaSr2Mn2O7 by Raman spectroscopy as high as 340 K and with decreasing temperature they become static and form a charge ordered (CO) phase below TCO=210 K. In the static regime, superlattice reflections are observed through neutron and x-ray diffraction with a propagation vector (h+1/4,k-1/4,l). Crystallographic analysis of the CO state demonstrates that the degree of charge and orbital ordering in this manganite is weaker than the charge ordering in three dimensional perovskite manganites. A TN=170K a type-A antiferro…
Despite the great technological and scientific importance, a well-controlled coupled behavior in magnetoelectric multiferroic materials at room temperature remains challenging. We demonstrate that the self-ordered A2BBO6 (e.g., A = La, B = Mn, and B = Ni) double perovskites provide a unique alternative opportunity to control and/or to induce such behavior in oxides. In this paper, we outline and discuss the various challenges and bottleneck issues related to this class of materials using La2NiMnO6 as a prototype. Details of the synthesis strategies, using pulsed laser deposition as a central t…
We performed a first-principles study of the structural, vibrational, electronic and magnetic properties of NaMnF3 under applied isotropic pressure. We found that NaMnF3 undergoes a reconstructive phase transition at 8 GPa from the Pnma distorted perovskite structure toward the Cmcm post-perovskite structure. This is confirmed by a sudden change of the Mn-F-Mn bondings where the crystal goes from corner shared octahedra in the Pnma phase to edge shared octahedra in the Cmcm phase. The magnetic ordering also changes from a G-type antiferromagnetic ordering in the Pnma phase to a C-type antiferr…
Direct visualization of ultrafast coupling between charge carriers and lattice degrees of freedom in photo-excited semiconductors has remained a long-standing challenge and is critical for understanding the light-induced physical behavior of materials under extreme non-equilibrium conditions. Here, by monitoring the evolution of the wave-vector resolved ultrafast electron diffraction intensity following above-bandgap photo-excitation, we obtain a direct visual of the structural dynamics in monocrystalline 2D perovskites. Analysis reveals a surprising, light-induced ultrafast lattice ordering r…
We introduce an electrostatic model including charge transfer, which is shown to account for the observed B-site ordering in Pb-based perovskite alloys. The model allows charge transfer between A-sites and is a generalization of Bellaiche and Vanderbilt's purely electrostatic model. The large covalency of Pb^{2+} compared to Ba^{2+} is modeled by an environment dependent effective A-site charge. Monte Carlo simulations of this model successfully reproduce the long range compositional order of both Pb-based and Ba-based complex A(BB^{'}B^{''})O_3 perovskite alloys. The models are also extended …
Single crystals of electron-doped SrMnO3 with a cubic perovskite structure have been systematically investigated as the most canonical (orbital-degenerate) double-exchange system, whose ground states have been still theoretically controversial. With only 1-2% electron doping by Ce substitution for Sr, a G-type antiferromagnetic metal with a tiny spin canting in a cubic lattice shows up as the ground state, where the Jahn-Teller polarons with heavy mass are likely to form. Further electron doping above 4%, however, replaces this isotropic metal with an insulator with tetragonal lattice distorti…
Double perovskites provide a unique opportunity to induce and control multiferroic behaviors in oxide systems. The appealing possibility to design materials with a strong coupling between the magnetization and the polarization fields may be achieved in this family since these magnetic insulators can present structural self-ordering in the appropriate growth conditions. We have studied the functional properties of La2CoMnO6 and Bi2CoMnO6 epitaxial thin films grown by pulsed laser deposition. Cation-ordered La2CoMnO6 films display a magnetic Curie temperature of 250 K while cation-disordered Bi2…
A model of localized classical electrons coupled to lattice degrees of freedom and, via the Coulomb interaction, to each other, has been studied to gain insight into the charge and orbital ordering observed in lightly doped manganese perovskites. Expressions are obtained for the minimum energy and ionic displacements caused by given hole and electron orbital configurations. The expressions are analyzed for several hole configurations, including that experimentally observed by Yamada et al. in La_{7/8}Sr_{1/8}MnO_3. We find that, although the preferred charge and orbital ordering depend sensiti…
We report cooperative magnetic orderings in a 6H-perovskite multiferroic system, Ba3HoRu2O9, via comprehensive neutron powder diffraction measurements. This system undergoes long-range antiferromagnetic ordering at TN1 ~ 50 K with a propagation wave vector of K1 = (0.5 0 0), a transition temperature much higher than the previously reported one at ~10 K (TN2). Both Ru and Ho-moments order simultaneously below TN1, followed by spin-reorientations at lower temperatures, demonstrating strong Ru(4d)-Ho(4f) magnetic correlation. Below TN1 another magnetic phase with a propagation wave vector K2 = (0…
Magnetic structures and the relationship between spin and charge-orbital orderings of an A-site ordered double-perovskite manganite SmBaMn2O6, an anticipated multiferroic material, were investigated by means of neutron diffraction. The spin arrangement in MnO2 planes perpendicular to the c axis is revealed to be the same as that in the A-site disordered half-doped manganites CE-type but the stacking pattern is found to be different displaying a unique twofold period. The temperature dependence of the superlattice magnetic and nuclear reflections clarifies that the antiferromagnetic spin orderi…
Multiferroics where at least two primary ferroic orders are present and coupled in a single system constitute an important class of materials. They attracted special consideration as they present both intriguing fundamental physics problems and technological importance for potential multifunctional devices. Here, we present the evidence of multiferroicity and magnetoelectric (ME) coupling in alpha-Mn2O3; a unique binary perovskite. Corresponding to the antiferromagnetic (AFM) ordering around 80K, a clear frequency independent transition is observed in the dielectric permittivity. We showed tha…
A unified theory is developed to explain various types of electronic collective behaviors in doped manganites R$_{1-x}$X$_x$MnO$_3$ (R = La, Pr,Nd etc. and X = Ca, Sr, Ba etc.). Starting from a realistic electronic model, we derive an effective Hamiltonianis by ultilizing the projection perturbation techniques and develop a spin-charge-orbital coherent state theory, in which the Jahn-Teller effect and the orbital degeneracy of e$_g$ electrons in Mn ions are taken into account. Physically, the experimentally observed charge ordering state and electronic phase separation are two macroscopic quan…
Here we report the magnetic and heat capacity studies of the double perovskite com-pounds Ba2SmRuO6 and Ba2DyRuO6. Antiferromagnetic transitions are inferred at 54 K and 47 K in Ba2SmRuO6 and Ba2DyRuO6, respectively in the magnetization measure-ments. Heat capacity measurements show large jumps at the corresponding temperatures and confirm the bulk magnetic ordering. Both the measurements provide clear indication of the ordering of the rare earth moments also along with the Ruthenium moments. How-ever, the heat capacity results suggest that the ordering of rare earth magnetic moments is spread…
We report density functional theory (DFT) investigation of $B$-site doped CaFeO$_3$, a prototypical charge-ordered perovskite. At 290 K, CaFeO$_3$ undergoes a metal-insulator transition and a charge disproportionation reaction 2Fe$^{4+}$$\rightarrow$Fe$^{5+}$+Fe$^{3+}$. We observe that when Zr dopants occupy a (001) layer, the band gap of the resulting solid solution increases to 0.93 eV due to a 2D Jahn-Teller type distortion, where FeO$_6$ cages on the $xy$ plane elongate along $x$ and $y$ alternatively between neighboring Fe sites. Furthermore, we show that the rock-salt ordering of the Fe$…
We demonstrate that ethylammonium copper chloride, (C2H5NH3)2CuCl4, a member of the hybrid perovskite family is an electrically polar and magnetic compound with dielectric anomaly around the Curie point (247 K). We have found large spontaneous electric polarization below this point accompanied with a color change in the sample. The system is also ferroelectric, with large remnant polarization (37μC/cm2) that is comparable to classical ferroelectric compounds. The results are ascribed to hydrogen-bond ordering of the organic chains. The coexistence of ferroelectricity and dominant ferromagnetic…
Single phase polycrystalline sample of perovskite Sr2TiMnO6 (STMO) has been successfully synthesized via solid state reaction route. Its detailed structural and physical properties have been studied using x-ray diffraction, transmission electron microscopy, magnetization, specific heat, and dielectric measurements. Rietveld analysis of the powder XRD data and transmission electron microscopy studies confirm that STMO is not a double perovskite structure with Fm-3m space group. But it is a disordered perovskite structure with Pm-3m space group where Ti4+ and Mn4+ ions are randomly distributed a…
The discovery of unusual negative thermal expansion (NTE) provides the opportunity to control the common but much desired property of thermal expansion, which is valuable not only in scientific interests but also in practical applications. However, most of the available NTE materials are limited to a narrow temperature range, and the NTE effect is generally weakened by means of various modifications. Here, we report an enhanced NTE effect that occurs over a wide temperature range (αV = -5.24 * 10-5 °C^-1, 25-575 ° C), and this NTE effect is accompanied by an abnormal enhanced tetragonality, a …
