The molybdate oxides SrMoO$_3$, PbMoO$_3$, and LaMoO$_3$ are a class of metallic perovskites that exhibit interesting properties including high mobility, and unusual resistivity behavior. We use first-principles methods based on density functional theory to explore the electronic, crystal, and magnetic structure of these materials. In order to account for the electron correlations in the partially-filled Mo $4d$ shell, a local Hubbard $U$ interaction is included. The value of $U$ is estimated via the constrained random-phase approximation approach, and the dependence of the results on the choice of $U$ are explored. For all materials, GGA+$U$ predicts a metal with an orthorhombic, antiferromagnetic structure. For LaMoO$_3$, the $Pnma$ space group is the most stable, while for SrMoO$_3$ and PbMoO$_3$, the $Imma$ and $Pnma$ structures are close in energy. The $R_4^+$ octahedral rotations for SrMoO$_3$ and PbMoO$_3$ are found to be overestimated compared to the experimental low-temperature structure.
A novel approach for finding new transparent conductors involves taking advantage of electronic correlations in metallic transition metal oxides, such as SrVO$_3$, to enhance the electronic effective mass and suppress the plasma frequency ($ω_P$) to infrared. Success of this approach relies on finding a compound with the right electron effective mass and quasiparticle weight $Z$. Biaxial strain can in principle be a fruitful way to manipulate the electronic properties of materials to tune both of these quantities. In this study, we elucidate the behavior of the electronic properties of early t…
We have successfully grown cm3-size single crystals of the metallic-ferromagnet Sm2Mo2O7 by the floating-zone method using an infrared-red image furnace. The growth difficulties and the remedies found using a 2-mirror image furnace are discussed. Magnetization studies along the three crystalline axes of the compound are presented and discussed based on our recent proposal of an ordered spin-ice ground state for this compound
Metal halide perovskites have recently emerged as promising materials for the next generation of optoelectronic devices owing to their remarkable intrinsic properties. In the growth of perovskite crystals, the substrates are essential and play a vital role. Herein, substrate engineering in the growth of perovskite crystals have been reviewed. Particularly, various modified strategies and corresponding mechanism based on the substrate engineering applied to the optimization of thickness, nucleation and growth rate are highlighted. Then the alterable adhesion to substrates will also be discussed…
Bismuth molybdate (BMO) is the simplest compound of aurivillius familywith a wide range of application as a tunable capacitor and sensor. The present article deals with the study of astructural, optical and catalytic property of tungsten doped Bismuth molybdate. The crystal structure is critically studied by Rietveld structural refinement method by using X-ray powder diffraction data. Raman scattering indicates that the structural distortion in BMO is mainly due to the rigid rotation of MoO6 octahedra. Due to the introduction of tungsten, the system experienced an increase in the band gap, whi…
Strain-induced suppression of thermochromism in divalent cobalt molybdate thin films
Robinson Research Institute, Victoria University of Wellington（惠灵顿维多利亚大学罗宾逊研究所）；Department of Physics, Photon Factory, University of Auckland（奥克兰大学物理系光子工厂）；Te Whai Ao Dodd-Walls Centre for Photonic and Quantum Technologies（Te Whai Ao 多德-沃尔斯光子和量子技术中心）；MacDiarmid Institute for Advanced Materials and Nanotechnology（麦克迪尔米德先进材料与纳米技术研究所）；O.O. Galkin Donetsk Institute for Physics and Engineering NAS of Ukraine（乌克兰国家科学院 O.O. 加尔金顿涅茨物理工程研究所）；Univ. Bordeaux, CNRS, Bordeaux INP, ICMCB, UMR5026（波尔多大学、法国国家科学研究中心、波尔多国立理工学院、波尔多材料化学研究所）；National Isotope Centre, Earth Sciences New Zealand（新西兰地球科学国家同位素中心）；THz/Far-IR Beamline, Australian Synchrotron（澳大利亚同步辐射加速器太赫兹/远红外光束线）
Halide perovskites are recently emerged as one of the frontline optoelectronic materials for device applications and have been extensively studied in past few years. Among these while, lead-based materials were most widely explored, investigation of optical properties of lead-free perovskites is limited. Being optically active, these materials were expected to show light-induced enhanced photoconductivity and the same was reported for lead halide perovskite single crystals. However, on contrary, herein, light-induced degradation of bismuth halide perovskite Cs3Bi2Cl9 single crystals is reporte…
The single phase polycrystalline Ba1/4Sr3/4MnO3 layered perovskite manganite has been synthesized by combustion method having various crystallite sizes. The room temperature X-ray diffraction patterns reveal that Ba1/4Sr3/4MnO3 crystallizes into hexagonal crystal structure with space group P63/mmc as confirmed by Rietveld refinement. The scanning electron micrographs of Ba1/4Sr3/4MnO3 reveal uniform crystallite size of the samples. Effect of crystallite size on lattice strain and crystal structure has been studied using Rietveld refinement and Williamson-Hall plot, respectively. The structural…
Organic-inorganic halide perovskites, especially methylammonium lead halide, have recently led to a remarkable breakthrough in photovoltaic devices. However, due to the environmental and stability concerns of the heavy metal, lead, in these perovskite based solar cells, research in the non-lead perovskite structures have been attracting increasing attention. In this study, a layered perovskite-like architecture, (NH4)3Bi2I9, was prepared in solution and the structure was solved by single crystal X-ray diffraction. The results from DFT calculations showed the significant lone pair effect of the…
Methylammonium lead iodide perovskite has attracted intensive interest for its diverse optoelectronic applications. However, most studies to date have been limited to bulk thin films that are difficult to implement for integrated device arrays because of their incompatibility with typical lithography processes. We report the first patterned growth of regular arrays of perovskite microplate crystals for functional electronics and optoelectronics. We show that large arrays of lead iodide microplates can be grown from an aqueous solution through a seeded growth process and can be further intercal…
We report the first single crystal growth of the correlated metal LaNiO3 using a high-pressure optical-image floating zone furnace. The crystals were studied using single crystal/powder x-ray diffraction, resistivity, specific heat, and magnetic susceptibility. The availability of bulk LaNiO3 crystals will (i) promote deep understanding in this correlated material, including the mechanism of enhanced paramagnetic susceptibility, and (ii) provide rich opportunities as a substrate for thin film growth such as important ferroelectric and/or multiferroic materials. This study demonstrates the powe…
Single crystals of a new twinned hexagonal perovskite compound Sr8Os6.3O24 have been synthesized, and structural and magnetic properties have been determined. The compound crystallizes in a hexagonal cell with lattice parameters a = 9.6988(3) Å and c = 18.1657(5) Å. The structure is an eight-layered hexagonal B-site deficient perovskite with the layer sequence (ccch)2 and represents the first example of a hexagonal structure among 5d oxides adopting a twin option. The sample shows spontaneous ferromagnetic magnetization below 430 K with a small saturation moment of 0.11 μB/Os ion. This is the …
In this study, different electronic structure evolutions of perovskite single crystals are found via angle-resolved photoelectron spectroscopy (ARPES): (i) unchanged top valence band (VB) dispersions under different temperatures can be found in the CH3NH3PbI3, (ii) phase transitions induced the evolution of top VB dispersions, and even a top VB splitting with Rashba effects can be observed in the CH3NH3PbBr3. Combined with low-energy electron diffraction (LEED), metastable atom electron spectroscopy (MAES), and DFT calculation, we confirm different band structure evolutions observed in these t…
Hybrid metal-organic perovskite solar cells have astounded the solar cell community with their rapid rise in efficiency over the past three years. Despite this success, the basic processes governing the photogeneration of free charges, particularly their dynamics and efficiency, remain unknown. Here we use ultrabroadband pulses of THz frequency light to see the intrinsic photophysical properties of single crystal lead halide perovskite just femtoseconds after a photon is first absorbed. Our spectra reveal the dynamics and efficiencies of free charge creation, the remarkable ease in which they …
We report an investigation of perovskite-type SmScO3 and NdScO3 single crystals by Raman scattering in various scattering configurations and at different wavelengths. The reported Raman spectra, together with the phonon mode assignment, set the basis for the use of Raman scattering for the structural investigation of RE-scandates. Further to the phonon signature, a fluorescence signal is observed for both scandates and is particularly intense for NdScO3 when using a 488 or 514 nm excitation line. A comparison of Raman spectra of RE-scandates with literature Raman data on orthorhombic perovskit…
Two new perovskite oxychalcogenides, Ca2CuFeO3S and Ca2CuFeO3Se, have been synthesized in evacuated quartz tubes. They crystallize in P4/nmm space group with lattice parameters a = 3.8271(1), c = 14.9485(2) Å and a = 3.8605(1), c = 15.3030(2) Å for Ca2CuFeO3S and Ca2CuFeO3Se, respectively. They appear to be the first layered chalcogenide perovskites involving calcium and are structural analogs of the corresponding Sr and Ba compounds. The new compounds exhibit semiconducting properties with energy gap decreasing from the oxysulfide to the oxyselenide. Possibility of introducing Ca2+ into struc…
Using nanoprobe X-ray diffraction microscopy, we investigate the relationship between residual strains from crystal growth in CsPbBr$_3$ thin film crystals, their stability, and local bandgap. We find that out-of-plane compressive strain that arises from cooldown from crystallization is detrimental to material stability under X-ray irradiation. We also find that the optical photoluminescence red shifts as a result of the out-of-plane compressive strain. The sensitivity of bandgap to strain suggests possible applications such as stress-sensitive sensors. Mosaicity, the formation of small misori…
An ab initio LMTO approach and semi-empirical quantum chemical INDO method have been used for supercell calculations of basic point defects - F-type centers and hole polarons bound to cation vacancy - in partly covalent perovskite KNbO3. We predict the existence of both one-site and two-site (molecular) polarons with close absorption energies (~ 1 eV). The relevant experimental data are discussed and interpreted.
Over the last few years of the heyday of hybrid halide perovskites, so many metal cations additives have been tested to improve their optoelectronic properties that it is already difficult to find an element that has not yet been tried. In general, the variety of these approaches is united under the name "doping", however, there is currently no clear understanding of the mechanisms of the influence of the metal ion additives on the properties of the lead halide perovskite materials. For many ions there is even no consensus on the most fundamental questions: what lattice position does a given i…
The layered perovskite YBaCuFeO5 (YBCFO) is able to adopt chiral magnetic order up to unexpectedly high temperatures, paving the way to strong magnetoelectric coupling at room temperature. In this perovskite A-site cations are fully ordered whereas the occupancy of the B-sites strongly depend on the preparation process. Though the structure is not geometrically frustrated, the presence of partial Fe3+/Cu2+ disorder at the B-sites produces magnetic frustration. In an effort to increase the spin-orbit coupling in the system, we have synthesized and studied YBaCuFe0.95Mn0.05O5 in single crystal f…
Here, we report structural and optical properties of (ALa)(FeMn)O6 (A = Ba and Sr) double perovskite synthesized via auto-combustion followed by a calcination process. Rietveld refinement of the structure using x-ray diffraction data reveals that (BaLa)(FeMn)O6 crystallizes into cubic crystal structure with space group Pm-3m while (SrLa)(FeMn)O6 crystallizes into rhombohedral crystal structure having space group R-3c. The absorption spectrum measurement using UV-Vis spectroscopy reveals that these samples are perfect insulator having an energy band gap between conduction and valence band of th…
Based on the reported ion migration under electric field in hybrid lead halide perovskites we have developed a bright, light emitting electrochemical cell with CH3NH3PbBr3 single crystals directly grown on vertically aligned carbon nanotube (VACNT) forests as contact electrodes. Under the applied electric field, charged ions in the crystal drift and accumulate in the vicinity of the electrodes, resulting in an in operando formed p-i-n heterojunction. The decreased interface energy barrier and the strong charge injection due to the CNT tip enhanced electric field, result in a bright green light…
Based on differential thermal analysis (DTA) and X-ray powder diffraction (XRD), a description of the system Nd$_2$O$_3$--Lu$_2$O$_3$--Sc$_2$O$_3$ was obtained by thermodynamic assessment. Four fields of primary crystallization could be identified; from melt compositions close to the Lu$_2$O$_3$--Sc$_2$O$_3$ edge the rare-earth oxide C-phase crystallizes first, which is stable down to room temperature. From Nd$_2$O$_3$ rich melts the X-phase forms, which is stable only at high temperatures. An additional field, where the alternative high-temperature phase H solidifies as primary product touche…
Organic-inorganic halide perovskites have been intensively re-investigated due to their applications, yet the opto-electronic function of the organic cation remains unclear. Through organic-selective resonant Auger electron spectroscopy measurements on well-defined single crystal surfaces, we find evidence for electronic coupling in the unoccupied states between the organic and inorganic sub-lattices of the prototypical hybrid perovskite, which is contrary to the notion based on previous studies that the organic cation is electronically inert. The coupling is relevant for electron dynamics in …
ABO3 oxides with the perovskite-related structures are attracting significant interest due to their promising physical and chemical properties for many applications requiring tunable chemistry, including fuel cells, catalysis, and electrochemical water splitting. Here we report on the crystal structure of the entire family of perovskite oxides with ABO3 stoichiometry, where A and B are Ba, Sr, Mn, Ce. Given the vast size of this chemically complex material system, exploration for stable perovskite-related structures with respect to its constituent elements and annealing temperature is performe…
Main physical characteristics, crystal, magnetic and electronic structures, of cerium-based perovskites CeTmO3 [Tm3+ = Sc, Ti, V] are systematically investigated via the first-principles computations. Full-potential linear augmented plane-wave with the local density approximation and generalized gradient approximation, under Perdew-Burke-Ernzerh and Wu-Cohen, based on DFT. The optimized crystal parameters indicate that the crystal of compounds can categorized under cubic structure (space group Pm-3m, no. 221), and their obtained lattice constants in good agreement with the available experiment…
We theoretically investigate the low-temperature phase of the recently synthesized Lu$_2$Mo$_2$O$_5$N$_2$ material, an extraordinarily rare realization of a $S=1/2$ three-dimensional pyrochlore Heisenberg antiferromagnet in which Mo$^{5+}$ are the $S=1/2$ magnetic species. Despite a Curie-Weiss temperature ($Θ_{\rm CW}$) of $-121(1)$ K, experiments have found no signature of magnetic ordering $or$ spin freezing down to $T^*\approx0.5$ K. Using density functional theory, we find that the compound is well described by a Heisenberg model with exchange parameters up to third nearest neighbors. The…
We have studied the temperature dependence of low-field magnetoresistance and current-voltage characteristics of a low-angle bi-crystal grain boundary junction in perovskite manganite La_{2/3}Sr_{1/3}MnO_3 thin film. By gradually trimming the junction we have been able to reveal the non-linear behavior of the latter. With the use of the relation M_{GB} \propto M_{bulk}\sqrt{MR^*} we have extracted the grain boundary magnetization. Further, we demonstrate that the built-in potential barrier of the grain boundary can be modelled by V_{bi}\propto M_{bulk}^2 - M_{GB}^2. Thus our model connects the…
Despite soaring performance of organic-inorganic hybrid perovskite materials in recent years, the mechanism of their decomposition at actual operation condition has been elusive. Herein, we elucidated the decrystallization process of CH3NH3PbI3 perovskite crystals via localized charges and identified polarity-dependent degradation pathway by carrying out time-evolution measurements for absorption spectra of perovskite films with underlying different charge transport layers and ab initio molecular dynamics calculations. It was found that the carrier polarity (hole-rich or electron-rich) inside …
Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the organic molecular cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low frequency Raman scattering with first-principles molecular dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in both hybrid (CH$_3$NH$_3$PbBr$_3$) and all-inorganic (CsPbBr$_3$) lead-halide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead…
Methylammonium lead triiodide (CH3NH3PbI3) perovskite solar cell is a gem in the list of photovoltaic semiconductors. Although there are numerous fundamental and technological questions yet to be addressed covering various aspects of this system for its commercialization, this study has employed first-principles DFT to model the [PbI6(CH3NH3)n]m zero-dimensional nanoclusters. Using the calculated binding energy landscapes, it has answered the question: why the corner-sharing PbI6 octahedron is surrounded by eight units of the organic cation in the large-scale supramolecular structures of the C…
The electronic structure of the cleaved perovskite (CH3NH3PbBr3) single crystal was studied in an ultra-high vacuum (UHV) system by angle-resolved photoemission spectroscopy (ARPES) and inverse photoelectron spectroscopy (IPES). Highly reproducible dispersive features of the valence bands were observed with nice symmetry about the Brillouin zone center and boundaries. The largest dispersion width was found to be ~0.73 eV and ~0.98 eV along the ΓX and ΓM directions, respectively. The effective mass of the holes was estimated to be ~0.59 m0. The quality of the surface was verified by atomic forc…
The remarkable optoelectronic, and especially photovoltaic performance of hybrid-organic-inorganic perovskite (HOIP) materials drives efforts to connect materials properties to this performance. From nano-indentation experiments on solution-grown single crystals we obtain elastic modulus and nano-hardness values of APbX3 (A = Cs, CH3NH3 and X = I, Br). The Youngs moduli are about 14, 19.5 and 16 GPa, for CH3NH3PbI3, CH3NH3PbBr3 and CsPbBr3, respectively, lending credence to theoretically calculated values. We discuss possible relevance of our results to suggested self-healing, ion diffusion an…
The structures of the recently reported ordered perovskites SrLa(FeTi)O6 and BaLa(FeTi)O6 have been revisited using Rietveld analysis of the powder x-ray diffraction data. Our studies clearly show that earlier authors have incorrectly reported the tetragonal structure in the I4/m space group for SrLa(FeTi)O6 and the cubic structure in the Fm3m space group for BaLa(FeTi)O6. The correct structure is found to be orthorhombic in the Pnma space group for SrLa(FeTi)O6 while cubic in the Pm3m space group for BaLa(FeTi)O6. Thus the BaLa(FeTi)O6 is not an ordered double perovskite as the occupancies of…
The phonon spectra of calcium, strontium, barium, radium, cadmium, zinc, magnesium, germanium, tin, and lead titanates with the perovskite structure are calculated from first principles within the density functional theory. By analyzing the unstable modes in the phonon spectra, the possible lattice distortions are determined and the energies of the corresponding phases are calculated. From analyzing the phonon spectra, force constants, and eigenvectors of TO phonons, a conclusion is drawn on the origin of the ferroelectricity in considered crystals. It is shown that the main factors determinin…
Two-dimensional (2D) perovskite materials have recently re-attracted intense research interest for applications in photovoltaics and optoelectronics. As a consequence of the dielectric and quantum confinement effect, they show strongly bound and stable excitons at room temperature. In this report, the band-edge exciton fine structure and in particular its exciton and biexciton dynamics in high quality crystals of (PEA)2PbI4 are investigated. A comparison of bulk and surface exciton lifetimes yields a room temperature surface recombination velocity of 2x10^3cm/s and an intrinsic lifetime of 185…
The crystal structures of the Sr1-xCaxRuO3 perovskites are investigated using both long range and local structural probes. High resolution synchrotron powder X-ray diffraction characterization at ambient temperature shows that the materials are orthorhombic to high precision, and we support previous work showing that Ca2+ substitution for Sr2+ primarily changes the tilting of rigid corner-sharing RuO6 octahedra at their shared oxygen vertices. X-ray pair distribution function analysis for SrRuO3, CaRuO3 and one intermediate composition show them to be locally monoclinic, and no long range or l…
We present a temperature dependent single crystal x-ray diffraction study of twinned orthorhombic perovskites La1-xCaxMnO3, for x=0.16 and x=0.25. These data show the evolution of the crystal structure from the ferromagnetic insulating state to the ferromagnetic metallic state. The data are modelled in space group Pnma with twin relations based on a distribution of the b axis over three perpendicular cubic axes. The twin model allows full structure determination in the presence of up to six twin fractions using the single crystal x-ray diffraction data.
We describe a first open-access database of experimentally investigated hybrid organic-inorganic materials with two-dimensional (2D) perovskite-like crystal structure. The database includes 515 compounds, containing 180 different organic cations, 10 metals (Pb, Sn, Bi, Cd, Cu, Fe, Ge, Mn, Pd, Sb) and 3 halogens (I, Br, Cl) known so far and will be regularly updated. The database contains a geometrical and crystal chemical analysis of the structures, which are useful to reveal quantitative structure-property relationships for this class of compounds. We show that the penetration depth of spacer…
We investigate the structural, electronic and optical properties of mixed bromide-iodide lead perovskite solar cell CH$_3$NH$_3$Pb(I$_{1-x}$Br$_x$)$_3$ by means of the virtual crystal approximation (VCA) within density functional theory (DFT). Optimizing the atomic positions and lattice parameters increasing the bromide content $x$ from 0.0 to 1.0, we fit the calculated lattice parameter and energy band gap to the linear and quadratic function of Br content, respectively, which are in good agreement with the experiment, respecting the Vegard's law. With the calculated exciton binding energy an…
Hybrid perovskite thin films have demonstrated impressive performance for solar energy conversion and optoelectronic applications. However, further progress will benefit from a better knowledge of the intrinsic photophysics of materials. Here, the low temperature emission properties of CH3NH3PbI3 single crystals are investigated and compared to those of thin polycrystalline films by means of steady-state and time-resolved photoluminescence spectroscopy. While the emission properties of thin films and crystals appear relatively similar at room temperature, low temperature photoluminescence spec…
We use resonant and non-resonant X-ray diffraction measurements in combination with first-principles electronic structure calculations and Monte Carlo simulations to study the relationship between crystal structure and multiferroic orders in the orthorhombic perovskite manganites, o-$R$MnO$_3$ ($R$ is a rare-earth cation or Y). In particular, we focus on how the internal lattice parameters (Mn-O bond lengths and Mn-O-Mn bond angles) evolve under chemical pressure and epitaxial strain, and the effect of these structural variations on the microscopic exchange interactions and long-range magnetic…
Tail state formation in solar cell absorbers leads to a detrimental effect on solar cell performance. Nevertheless, the characterization of the band tailing in experimental semiconductor crystals is generally difficult. In this article, to determine the tail state generation in various solar cell materials, we have developed a quite general theoretical scheme in which the experimental Urbach energy is compared with the absorption edge energy derived from density functional theory (DFT) calculation. For this purpose, the absorption spectra of solar cell materials, including CdTe, CuInSe2 (CISe)…
We report calculations indicating that amorphous RAO$_3$ oxides, with R and A trivalent cations, have approximately the same static dielectric constant as their perovskite crystal phase. The effect is due to the disorder-activated polar response of non-polar crystal modes at low frequency, which compensates a moderate but appreciable reduction of the ionic dynamical charges. The dielectric response was studied via density-functional perturbation theory. Amorphous samples were generated by molecular dynamics melt-and-quench simulations.
We report a strongly temperature dependent luminescence Stokes shift in the electronic spectra of both hybrid and inorganic lead-bromide perovskite single crystals. This behavior stands in stark contrast to that exhibited by more conventional crystalline semiconductors. We correlate the electronic spectra with the anti-Stokes and Stokes Raman vibrational spectra. Dielectric solvation theories, originally developed for excited molecules dissolved in polar liquids, reproduce our experimental observations. Our approach, which invokes a classical Debye-like relaxation process, captures the dielect…
The question of the origin of the piezoelectric properties enhancement in perovskite ferroelectrics is approached by analyzing the Gibbs free energy of tetragonal BaTiO3, PbTiO3 and Pb(Zr,Ti)O3 in the framework of the Landau-Ginzburg-Devonshire theory. The flattening of the Gibbs free energy profile appears as a fundamental thermodynamic process behind the piezoelectric enhancement. The generality of the approach is demonstrated by examining the free energy flattening and piezoelectric enhancement as a function of composition, temperature, electric field and mechanical stress. It is shown that…
Nuclear site analysis methods are used to enumerate the normal modes of $ABX_{3}$ perovskite polymorphs with octahedral rotations. We provide the modes of the fourteen subgroups of the cubic aristotype describing the Glazer octahedral tilt patterns, which are obtained from rotations of the $BX_{6}$ octahedra with different sense and amplitude about high symmetry axes. We tabulate all normal modes of each tilt system and specify the contribution of each atomic species to the mode displacement pattern, elucidating the physical meaning of the symmetry unique modes. We have systematically generate…
Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) are promising candidates for optoelectronic applications due to their efficient light emission properties, and strong dielectric confinement effects. Raman spectroscopy is a versatile, non-contact and often non-destructive technique, widely used to characterize crystalline materials. However, the inherently weak phonon scattering, strong background, and complex nature of the Raman signals from HOIPs present challenges in obtaining reliable signals. Further, the fragile nature of the 2D HOIP crystals results in rapid degradation …
We present an approach to the implementation of the virtual crystal approximation (VCA) for the study of properties of solid solutions in the context of density-functional methods. Our approach can easily be applied to any type of pseudopotential, and also has the advantage that it can be used to obtain estimates of the atomic forces that would arise if the real atoms were present, thus giving insight into the expected displacements in the real alloy. We have applied this VCA technique within the Vanderbilt ultrasoft-pseudopotential scheme to predict dielectric and piezoelectric properties of …
Perovskite chalcogenides are gaining substantial interest as an emerging class of semiconductors for optoelectronic applications. High quality samples are of vital importance to examine their inherent physical properties. We report the successful crystal growth of the model system, BaZrS$_3$ and its Ruddlesden-Popper phase Ba$_3$Zr$_2$S$_7$ by flux method. X-ray diffraction analyses showed space group of $Pnma$ with lattice constants of $a$ = 7.056(3) Å\/, $b$ = 9.962(4) Å\/, $c$ = 6.996(3) Å\/ for BaZrS$_3$ and $P4_2/mnm$ with $a$ = 7.071(2) Å\/, $b$ = 7.071(2) Å\/, $c$ = 25.418(5) Å\/ for Ba…
We report an investigation of DyScO3 and GdScO3 single crystals by Raman scattering in various scattering configurations and at various wavelengths. The Raman spectra are well-defined and the reported spectral signature together with the mode assignment sets the basis for the use of Raman scattering for the investigation of RE-scandates. The observed positions of Raman modes for DyScO3 are for most bands in reasonable agreement with recent theoretical ab initio predictions of the vibrational spectrum for the same material. Further to the phonon signature, a luminescence signal is observed for …
We have accurately determined the exciton binding energy and reduced mass of single crystals of methylammonium lead tri-iodide using magneto-reflectivity at very high magnetic fields. The single crystal has excellent optical properties with a narrow line width of $\sim 3$meV for the excitonic transitions and a 2s transition which is clearly visible even at zero magnetic field. The exciton binding energy of $16 \pm 2$meV in the low temperature orthorhombic phase is almost identical to the value found in polycrystalline samples, crucially ruling out any possibility that the exciton binding energ…
