Simple Perovskite Structure Research Articles

Hydride-Ion Conduction in AELiH3 (AE = Sr, Ba)

Hydride ions (H–) are expected to conduct fast in solids owing to their monovalent state, appropriate ionic radius for conduction, and large polarizability. Thus, H– is a promising class of the charge carrier with high mobility, and may be applicable to the electrochemical reaction in batteries and fuel cells. The K2NiF4–type structure, wherein the perovskite KNiF3 and the rock-salt KF layers are stacked along the c-axis, has been the most researched material as a hydride-ion conductor, e.g., K2NiF4–type oxyhydrides of La2–x–y Sr x +y LiH1–x+y O3–y [1]. In this study, we focused on perovskite-type hydrides, AELiH3 (AE = Ca, Sr, Ba). A simple perovskite structure is expected to have high ionic conductivity, because it ensures a three-dimensional diffusion pathway for the anion species [2-6].First, the migration energy of H– ions in the AELiH3 materials were evaluated using nudged elastic band (NEB) calculations. The migration pathway between adjacent H– sites via vacancies was considered. First-principles calculations were performed using the projector-augmented wave method and PBEsol functional as implemented in the VASP code. The H– diffusivity of sodium-doped SrLiH3 was investigated using density functional theory molecular dynamics. AELiH3 were experimentally synthesized using a mechanochemical method, and their ionic conductivities were evaluated using electrochemical impedance spectroscopy. To further improve the ionic conductivity of these materials, hydride-ion vacancies were introduced by replacing the A-site cation with the monovalent cation of Na+. Neutron powder diffraction (NPD) data were collected at room temperature using a time-of-flight diffractometer (BL09 SPICA) at the J-PARC facility. The distribution of the nuclear scattering length density was analyzed by the maximum entropy method (MEM) using the Z-MEM code. The effect of the alkali-earth element at A-site on the migration energy of H– was evaluated using NEB. The migration energy are estimated to be 24, 35, and 39 kJ mol–1 for CaLiH3, SrLiH3, and BaLiH3, respectively. These low migration energy (< 40 kJ mol–1) suggest that the perovskite-type AELiH3 are suitable substances for hydride-ion conduction. AELiH3 (AE = Sr, Ba) were synthesized via mechanical milling process. The X-ray diffraction patterns of SrLiH3 and BaLiH3 were attributed to a cubic perovskite structure with the space group Pm–3m. For CaLiH3, the starting materials of CaH2 and LiH remained in the product, and the perovskite-type CaLiH3 could not be synthesized. The ionic conductivities of SrLiH3 and BaLiH3 at 100 °C were 4.6 × 10–7 and 6.7 × 10–9 S cm–1, respectively. This clearly denotes the characteristic of hydride ion; a smaller ionic radius of the A-site cation results in a lower migration energy and a higher ionic conductivity. Solid solutions of Sr1–x Na x LiH3–x were obtained in the range of 0 ≤ x ≤ 0.075. The ionic conductivity was enhanced upon Na-doping. The highest conductivity was observed for Sr0.925Na0.075LiH2.925 (x = 0.075) with a bulk conductivity of 5.0 × 10–6 S cm–1 at 25.6 °C. The figure shows the refined crystal structure of Sr0.925Na0.075LiH2.925 obtained by a Rietveld analysis of the NPD data, in addition to the isosurface plot of the nuclear density obtained by MEM. Rietveld analysis confirmed the presence of H defects and a remarkable anisotropy of the thermal oscillations of H. The negative nuclear density at the H sites showed broadening along the {100} direction. These structural features suggest that hydride ions conduct via vacancies between their adjacent sites. The choice of small cations at the A sites and the presence of hydrogen vacancies in perovskite-type hydrides resulted in high hydride-ion conductivity. [1] Kobayashi et.al., Science, 351, 1314–1317(2016). [2] Bai, Q. et.al., ACS Appl. Energy Mater., 1, 1626–1634(2018). [3] Ishihara, T. et.al., J. Am. Chem. Soc., 116, 3801–3803(1994). [4] Li, M. et.al., Nat. Mater., 13, 31–35(2014). [5] Hull, S. et.al., J. Phys.: Condens. Matter, 11, 5257–5272(1999). [6] Yamane, Y. et.al., Solid State Ionics, 179, 605–610(2008). Figure 1

Enhancing structural properties of simple perovskite materials based on zirconate and titanate prepared by sol-gel method

A simple and effective method is used in this study in order to obtain lead and lead-free simple perovskite structures. The perovskite materials BaTiO3, BaZrO3, PbTiO3 and PbZrO3 were synthesized via the sol-gel method. The main aim of this study is to investigate the effects of calcination temperature and rate on the material's properties. The structural phase formation of the prepared materials was characterized using X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The results gathered show that perovskite compounds based on barium occur at higher crystallization temperature, 900 and 1000 °C for BaTiO3 and BaZrO3 respectively, than the ones based on lead, 680 °C for PbTiO3 and PbZrO3. On the other hand, zirconate materials begin to crystallize at relatively high temperatures (1000 °C for BaZrO3 and 680 °C PbZrO3), than titanate-based materials (900 °C for BaTiO3 and 600 °C for PbTiO3). Also, the results showed, the obtaining of the non-centrosymmetric perovskite structure, indicating that piezoelectric property is present for all the elaborated materials.

Electrospun Nanofiber Electrodes with in situ Exsolved Nanocatalysts for Symmetrical SOCs

Solid oxide cells (SOCs) offer great promise for efficient energy generation and storage in a variety of applications. Symmetrical SOCs with identical anode and cathode materials configuration favoring an efficient reversible operation of the cells, allow both electricity production from traditional and renewable energy sources in fuel cell mode, and clean, efficient fuel production (in reverse/electrolysis mode). In addition, the symmetrical cell design is particularly advantageous, including: decreased number of cell components, simplification of fabrication process and alleviating the chemical stability issues related with materials, as well as the enhanced resistance to coking and sulphur poisoning, when cells are fuelled by alternative sources (non-H2) [1]. However, electrode material candidates with excellent redox stability and electrocatalytic activities in both oxidizing and reducing conditions for symmetrical SOCs are limited due to the strict criteria. The design of electrode materials with in situ exsolution of nanoparticles significantly benefits the performance of SOCs [2]. In the anode operation condition, metallic nanoparticles are in situ exsolved from the parent electrode materials decorating on the electrode surface, substantially improving the catalytic activity and electronic conductivity of anode, thus boosting the cell performance. The in situ exsolved nanoparticles can be socketed to the parent oxide, enhancing the stability and hydrocarbon coking tolerance, making the symmetrical SOCs fuelled by cheaper and readily available non-hydrogen alternatives. Moreover, the possible reversible exsolution/dissolution of nanoparticles can potentially resolve the particle agglomeration and coke formation during usage of non-hydrogen fuels [2, 3]. The electrospinning technique has been reported to obtain nanofiber-structured electrodes for SOCs, which efficiently contributes to the enhancement of the electrochemical performance of SOCs [4].In this work, the A-site deficient (Ln, Ba/Sr)2-α(Fe,M)2-x(Ni,Co)xO6-δ (Ln = selected lanthanides; M = Mn, Ti, Cr, Mo, W) perovskites were successfully obtained and evaluated as novel electrode materials for SOCs. It has been found that the A-site nonstoichiometry favours the in situ exsolution of metallic nanocatalysts (NixCo) from the parent materials in reducing condition. The selection of A-site cations (lanthanides) significantly affects the crystal structure (simple or double perovskite structure), while the B-site cations determine the stability of materials in air and reducing atmospheres. The reversibility of exsolved nanoparticles is systematically investigated under reducing and oxidizing conditions with different annealing temperatures. The possibility of in situ exsolution of nanooxides on the cathode (NixCoOy-like nanooxides) is also investigated. Nanofiber-structured electrodes with the ability of in situ exsolution of nanocatalysts are fabricated using the electrospinning technique, which significantly boost the electrochemical properties of constructed SOCs.

Quantum Machine Learning in Materials Prediction: A Case Study on ABO3 Perovskite Structures.

Quantum machine learning (QML), ML on quantum computers, offers a promising approach for discovering and screening novel materials. This study introduces a hybrid classical-quantum ML method using a variational quantum classifier to identify simple perovskite structures within a data set of ABO3 compounds. The model is trained using a data set of 397 known ABO3 compounds, with 254 perovskites and 143 non-perovskite structures labeled as +1 and -1, respectively. By considering feature correlation and eliminating less important features, the QML system achieves an optimal accuracy of 88% for training data and 87% for unseen test data. These results demonstrate the potential of QML in materials science classification tasks, even with limited training data, leveraging the intrinsic properties of quantum computation to enhance the investigation of materials. In addition, perspectives on QML applications in materials science are discussed.

Synthesize, construction and enhanced performance of Bi2WO6/ZnS heterojunction under visible light: Experimental and DFT study

With the simple perovskite structure, Bi2WO6 could be utilized as a modifier to overcome the low visible light response of the wide energy band photocatalyst ZnS. Flower-like Bi2WO6 was simply synthesized by hydrothermal method and Bi2WO6/ZnS heterojunction was constructed via solvothermal reaction. The results showed that ZnS nanospheres were uniformly loaded on the flower-like structure, which was well kept under low concentration loading (≤20%ωt ZnS). The degradation of MB and Rh.B under visible light was used to measure the photocatalytic activity of the photocatalysts. The degradation rates of MB and Rh.B by 20%ωt-Bi2WO6/ZnS were as high as 94.3% and 92.8%, respectively. Moreover, the degradation performance of photocatalyst still maintained 89.3% after 4 times recycling tests. The visible light absorption ability of modified ZnS was improved, and the recombination of photogenerated electrons and holes was inhibited due to the formation of heterojunction. According to the data from density functional theory calculation, the composition of the valence band and conductive band of the Bi2WO6/ZnS system has been altered. The band gap of Bi2WO6/ZnS was reduced by roughly 1.12 eV compared to that of pure ZnS, and the work function analysis were in good agreement with the experimental results. Under light stimulation, electrons were transferred from Bi2WO6 to ZnS to produce superoxide radicals which played key roles in the degradation reaction of dyes.

Enhancement of Electrocatalytic Activity for both Hydrogen and Oxygen Evolution Reactions of a Perovskite Oxide

We have used both experimental and computational methods to show the significant impact of the incorporation of a 4d metal, Mo, into the perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), which is known as a benchmark electrocatalyst for the anodic reaction of water-splitting. We demonstrate the enhanced electrocatalytic properties of the resulting catalytic material, Ba0.5Sr0.5Co0.5Mo0.5O3 (BaSrCoMoO6), where the presence of the 4d metal Mo leads to the formation of a double perovskite structure, as opposed to the simple perovskite structure of BSCF. The consequence of this transformation is the enhancement of the electrocatalytic properties of BaSrCoMoO6 over BSCF for both half reactions of water-splitting, i.e., hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Furthermore, BaSrCoMoO6 shows electrocatalytic activity for HER and OER in bulk form without additives, even carbon black, which is commonly added to HER and OER catalysts, including BSCF. Experiments for BaSrCoMoO6 with or without carbon black lead to similar overpotentials. Density functional theory (DFT) calculations reveal the effect of the structural transformation on the shift of the transition metal d bands toward the Fermi level, which correlates with the enhanced electrocatalytic activity.

Synthesis and structural characterization of a novel perovskite oxyfluoride BaY0.5Zr0.5O2.5F0.5

In this study, a novel perovskite oxyfluoride BaY0.5Zr0.5O2.5F0.5 was prepared by a solid-state reaction using BaCO3, ZrO2, Y2O3 and BaF2 as raw materials. The synthetic process of BaY0.5Zr0.5O2.5F0.5, the effect of the mole ratio of raw materials, and sintering temperature on the phase composition were investigated, and the structure of BaY0.5Zr0.5O2.5F0.5 was characterized. The results indicated that the pure oxyfluoride compound BaY0.5Zr0.5O2.5F0.5 was successfully synthesized after sintering at 1400 °C for 24 h with 15% mol excess BaF2. The grains of BaY0.5Zr0.5O2.5F0.5 were of a regular columnar shape with a size of 0.5–2 μm. The space group of BaY0.5Zr0.5O2.5F0.5 was Pm-3m with a = 4.2819 Å. In this simple perovskite structure, Ba atoms occupied the body center of the structure, Y and Zr atoms were disordered in the B site, and O and F atoms were disordered in the X site, with the occupation of 83% O atoms and 17% F atoms. In addition, introducing F− ions into oxygen vacancies made BaY0.5Zr0.5O2.5F0.5 more stable and decreased the lattice content. This study provides new insights into the modification method of perovskite.

Topotactic Oxygen Release and Incorporation in AFeO3 with Fe4+, AFeO2.5 with Fe3+, and AFeO2 with Fe2+ (A = Ca and Sr): Dedicated to the Occasion of the 100th Birthday of Prof. John B. Goodenough

Oxygen contents in perovskite-structure Fe oxides can change in accordance with the valence states of Fe, i.e., AFeO3 with Fe4+, AFeO2.5 with Fe3+, and AFeO2 with Fe2+ (A = Ca and Sr). AFeO3 has a fully oxygenated simple-perovskite structure, and the unusual high valence Fe4+ in AFeO3 is easily reduced to relatively stable Fe3+ by releasing oxygen. On the other hand, AFeO2 has an infinite-layer structure, and the unusual square-planar coordination of Fe2+ in AFeO2 changes to tetrahedral and octahedral Fe3+ by incorporating oxygen. Sample weight measurements by thermogravimetry and corresponding phase analysis with synchrotron X-ray diffraction data revealed that the difference in the A-site cation strongly influenced the oxygen release and incorporation behaviors. In ambient air, topotactic changes of AFe4+O3 → AFe3+O2.5 ← AFe2+O2 for both A = Ca and Sr can occur by releasing and incorporating oxygen in the perovskite structure frameworks. Nonstoichiometric phases with oxygen vacancies are present between SrFeO3 and SrFeO2.5.

LaTiO2N nanopowders (NPs) with low surface defect density via nitridation of flame made NPs retaining simple perovskite structure.

This work introduces a novel route to perovskite LaTiO2N nanopowders (NPs) via nitridation of perovskite LaTiO3 NPs in an NH3 gas flow at 1050 °C/NH3/15 h, in which a simple perovskite structure (ABX3) is retained during nitridation. The LaTiO3 NP is formed with a trace of a second phase in a precursor oxide NP (LTO-4/3) produced using liquid-feed flame spray pyrolysis (LF-FSP) of a metallo-organic ethanol solution with La/Ti = 4/3. The characterization of the resulting powders allows for a comparison with LaTiO2N NPs synthesized by the nitridation of the La2Ti2O7 precursor oxide NP (LTO-1) with a perovskite slab structure (A2B2X7) also prepared by LF-FSP of a La/Ti = 1 solution. Williamson-Hall plots suggest that the as-produced LaTiO2N from LTO-1 offers a quite small but effective crystallite size of 16-18 nm with almost no lattice spacing fluctuations, while LaTiO2N from LTO-4/3 presents a larger effective crystallite size of 50-52 nm with some lattice spacing fluctuations. UV-vis diffuse reflectance analysis reveals that, unlike LaTiO2N from LTO-1, the spectra of LaTiO2N from LTO-4/3 show a quite low absorptionbackground above the wavelength of the optical absorption edge (∼580 nm), suggesting good crystallinity with a very low surface defect density. Both oxynitride NPs appear to offer utility as inorganic pigments with different colours, while LaTiO2N NPs from LTO-4/3 have advantages for various applications, including potential as a visible-light-driven water splitting photocatalyst.

Remarkably high proton conductivity in cubic perovskite-related Ba3WO6

Remarkably high proton conductivity was identified in a cubic Ba3WO6 polymorph with a 4 × 4 × 4 superstructure of a simple perovskite structure.

Sc3Ir4Si13+x and Sc4Ir7Ge6 – the perovskite-related crystal structures

Abstract The crystal structure of Sc3Ir4Si13+x (x = 0.22) [space group P m 3 ‾ n $Pm\bar{3}n$ , a = 8.4651(1) Å] is found to be a new disordered variant of the primitive cubic Yb3Rh4Sn13 Remeika prototype. The silicide is stable in the narrow temperature range of 1283–1397 °C and reveals metallic properties. The crystal structure of Sc4Ir7Ge6 [U4Re7Si6 type, space group I m 3 ‾ m $Im\bar{3}m$ , a = 8.1397(8) Å] is refined for the first time. The electronic band structure calculations reveal that the properties of this germanide can be explained based on the free electron gas model. Both compounds reveal close structural relationships to the simple perovskite structure.

The hydrogen-containing bronzes H0.23WO3 and H0.10ReO3 synthesized via a polymer route

We report the synthesis of two hydrogen-containing perovskite-type bronzes H0.23WO3 and H0.10ReO3 utilizing an unconventional solid-state synthetic approach, involving the use of the polymer Poly(vinylidene fluoride) (CH2CF2)n. Powder neutron diffraction at ambient temperature shows that H0.23WO3 crystallizes in a tetragonal symmetry distortion of the simple perovskite structure (space group P4/nmm), with lattice parameters a ​= ​5.2279(2) Å, and c ​= ​3.8763(1) Å. H0.10ReO3, in contrast, crystallizes in a monoclinic distortion of a simple cubic perovskite (space group P2/m), with lattice parameters a ​= ​5.3125(1) Å, b ​= ​5.3155(3) Å, c ​= ​3.7045(3) Å, and γ ​= ​90.43(1)°. Both H0.23WO3 and H0.10ReO3 exhibit intrinsically diamagnetic behavior, with low temperature paramagnetic upturns and no signs of bulk superconductivity down to 0.35 ​K.

Structural, dielectric and ferroelectric properties of lead free Gd-modified BiFeO3–BaTiO3 solid solution

Due to the high Curie temperature the rare-earth-modified bismuth ferrite (BiFeO3 or BFO) and/or its derivatives have uncomplicated lead-free chemistries and simple perovskite structures have attracted the materials community. So, in this report, structural, micro-structural, ferroelectric and electrical characteristics of a rare-earth (Gd)-modified perovskite BiFeO3–BaTiO3 solid solution, fabricated by a cost effective solid-state reaction technique, have been presented. The structural analysis using X-ray diffraction pattern and data indicates the evolution of a mono-phase distorted perovskite structure with the existence of rhombohedral structure. The ambient temperature scanning electron micrograph of Gd modified BiFeO3–BaTiO3 solid solution exhibits uniform grain distribution over the surface. The dielectric parameters are found to be frequency and temperature dependent. The well defined polarization–electric field hysteresis loop of the samples at room temperature suggest that Gd substitution at the Bismuth site of the solid solution strongly affects remnant and saturated polarization of the materials. The ac conductivity spectra obeys the Jonscher’s power law. Based on the derived parameters of Gd modified BiFeO3–BaTiO3 solid solution, it is expected to fabricate a functional device.

Synthesis, structure and magnetic properties of Ti doped La2MnNiO6 double perovskite

We report sol-gel synthesis, structural characterization and magnetic properties of La2Mn1-xTixNiO6 (0 ≤ x ≤ 1.0). Ti doping removed the biphasic structure of La2MnNiO6 by suppression of rhombohedral structure and all the Ti containing samples crystallized in monoclinic P21/n symmetry. La2MnNiO6 exhibits multiple magnetic transitions. The high temperature ferromagnetic transition of La2MnNiO6 gradually shifted to lower temperatures with increase in Ti doping. La2TiNiO6 (x = 1.0) does not show any long-range magnetic ordering. The suppression of magnetic transition by Ti doping is ascribed to the destruction of Mn4+—O—Ni2+ superexchange interaction. However, the signature of ferromagnetic phase persists up to 70% Ti doping, indicating the robustness of magnetic ordering in La2MnNiO6. These results suggest that the addition of Ti4+ truncates the ferromagnetic Mn4+—O—Ni2+ superexchange path and it likely promotes ferromagnetic cluster formation. The robustness of ferromagnetic state towards Ti substitution compared to the simple perovskite or spinel structure can be attributed to cationic ordering in double perovskite structure. Both the pure and Ti-doped samples exhibit magnetic frustration at lower temperatures due to partial cationic disordering. The absence of long-range ordering in La2TiNiO6, unlike La2TiCoO6 or Pr2TiCoO6, could be related to cationic disordering.

Proton Conducting Properties of Sr1+XLn1-XAlO4-δ (Ln=Pr,Sm) with Layered Perovskite Structure for Solid Oxide Fuel Cells

Perovskite material, such as SrCeO3,BaCeO3, SrZrO3 and BaZrO3 are expected for as electrolyte material of proton conductive SOFC due to their high proton conductivity at 500-700 ºC.[1] Proton conductive electrolyte is required not only high conductivity but also high ionic transport number, high proton transport number and high stability. BaCe1-xYxO3-δ(BCY) is reported as a high conductivity material but the chemical stability is not sufficient especially in CO2 atmosphere. Recently, we reported Pr doped Ba2In2O5(PBI)[2] for proton conducting SOFC. However, the SOFC with PBI demonstrated relatively low power density of 4.0mW/cm2 at 700○C. Therefore, the development of electrolyte material is still required for PC-SOFC. To develop the novel proton conductor, we focused on layered perovskite structures. We have reported the proton conductivity of Sr1+xPr1-xInO4-δ (SPI)[3], which has Ruddlesden-Popper structure (expressed in A’OAnBnO3n, when n=1 called as K2NiF4 structure). Due to introduction of rock salt layer (A’O layer), improving proton transport number was suggested due to the selective inhibition of oxide ion conduction and improvement of stability were also expected. With considering proton transport mechanism which is suggested as shown in Eq.1, the basicity (relating to electronegativity) of constituent element is also an index of proton transport number at high temperature by stabilizing OH-. As a result, the total conductivity of SPI was logσ≒-1.5 in 900 ºC in 8% humidified O2, and power generation was not stably operated at 500 ºC in H2 fuel. Their conductivity, stability and transport number in high temperature is a remaining issue to be improved. To improve conductivity and stability, we tentatively applied the tolerance factor of simple perovskite structure (Eq. 2) as an index of the structure symmetry of K2NiF4. When tolerance factor is near 1, the structure has good symmetry, so higher stability and better ionic conductivity is expected. For A and A’ site with large ionic radius and B site with small element are required to keep the tolerance factor near 1. Thus, in this work we chose Al for B site which has small ionic radius instead of In. Sr1+xPr1-xAlO4-δ (SPA) has good tolerance factor of 1.01. Moreover, we also focused on ionic valence which has the connection with oxygen deficiency to improve conductivity and proton transport number. Valence change will change amount of oxygen vacancy and which are estimated by Eq. 3-4. Pr ion is Pr3+ or Pr4+ and Sm ion is Sm3+ or Sm2+ .They have almost same ionic radius and electronegativity as shown in Table1. Therefore, we also investigated Sm instead of Pr for A site element to discuss the effect of ionic valence for the electrolyte properties. Sr1+xSm1-xAlO4-δ(SSA) also has good tolerance factor of 1.01. We synthesized SPA and SSA with different A/A’ ratio and observed their power generation characteristics to investigated the confirm the validity to use such index for the development of proton conductive materials. All samples were synthesized by solid phase reactions using the powders of Pr6O11, Sm2O3, Sr2CO3 and Al2O3 .After making the disk of SPA and SSA and sintering in 1400 ºC for 10 h, analysis of crystal structure was carried out by XRD measurement. The conductivities were measured by using AC impedance spectroscopy. Ionic transport numbers were evaluated by the configuration of H2 and O2 concentration cells. The power generation of SOFC with SPA and SSA electrolyte are carried out at 500 ~ 900℃. The total conductivities of SPA and SSA are lower than that of SPI in dry and humidify O2.On the other hand, SSA and SPA has proton conductivity and high proton transport number especially at 700 ~ 900 ºC. The power generation experiments using SOFC with the disks of SPA and SSA were carried out. [1] N. Kochetova et.al. RSC Adv., 2016, 6, 73222 [2]X.Li, M.Ihara, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 2015,162,8 [3]X.Li, H.Shimada, M.Ihara, ECS Transactions, 50(27), 3-14 (2013) Figure 1

Features of Highly Correlated Electronic States in the Simple Perovskite Manganite Sr1−xSmxMnO3 with 0.15 ≤ x ≤ 0.50

The C- and A-type antiferromagnetic orderings have been reported in the highly correlated electronic manganite Sr1−xSmxMnO3 (SSMO) with the simple perovskite structure in the composition range of 0.34 ≤ x ≤ 0.46. Because these antiferromagnetic orderings should be coupled to orbital orderings, the crystallographic features of SSMO samples prepared with 0.15 ≤ x ≤ 0.50 have been investigated, mainly by X-ray powder diffraction and transmission electron microscopy, to understand the detailed features of the corresponding orbital-ordered states. It was found that around 100 K, for instance, the C-type orbital-ordered (COO) state was observed for 0.15 ≤ x ≤ 0.42, the orbital-modulated (OM) state for 0.44 ≤ x < 0.50, and the coexistence state of both ferromagnetic Pnma (I) and paramagnetic Pnma (II) regions for x = 0.50, where the OM state was characterized by a transverse lattice modulation with an incommensurate periodicity. Neither the A-type orbital-ordered state nor the CE-type state involving both orbita...

Features of the Relaxor State in the Simple-Perovskite Mixed-Oxide System (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3

The mixed-oxide system (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) has a simple perovskite structure and exhibits relaxor behavior for 0 ≤ x ≤ 0.30 (low Ti contents). To understand the relaxor state in PMN–xPT, the crystallographic features of the ferroelectric states were investigated via transmission electron microscopy, taking advantage of Friedel’s law failure. Polar regions having 〈110〉C and 〈001〉C components were observed separately both below and near Tm, the maximum temperature of the dielectric permittivity for the relaxor. As a result, the relaxor state for 0 < x ≤ 0.30 was identified as an assembly of nanometer-scale polar domains with rhombohedral symmetry. On the other hand, the ferroelectric states for 0.40 ≤ x ≤ 0.70 are characterized by a ferroelectric MC-type monoclinic state, having a polarization vector in the {100}C planes. Thus, the FR/FMC boundary around x = 0.35 was identified as the morphotropic phase boundary (MPB), nearly parallel to the temperature axis.

Features of Electronic States in the Highly-Correlated Electronic System Sr&lt;sub&gt;1-&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Nd&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;MnO&lt;sub&gt;3&lt;/sub&gt; around &lt;i&gt;x &lt;/i&gt;= 0.50

In the highly-correlated electron system Sr1-xNdxMnO3 (SNMO) having the simple perovskite structure, there are interesting electronic states, which are related to degrees of charge, orbital, and spin freedoms for eg electrons in Mn ions. Among these states, in the case of SNMO, the C-, A-and CE-type antiferromagnetic states were reported for 0.20 ≤ x ≤ 0.38, for 0.38 ≤ x ≤ 0.48, and for 0.48 ≤ x ≤ 0.52, respectively. The points to note here are that these antiferromagnetic states are directly associated with corresponding orbital orderings, and that the CE-type state also accompanies charge ordering. Because of these features, we were interested in the (A → CE) state change in SNMO. The crystallographic features of prepared SNMO samples with 0.46 ≤ x ≤ 0.50 have thus been investigated mainly by means of a transmission electron microscope equipped with a low-temperature holder. As a result, the state around 100 K for x = 0.48 was first understood to be identified as the Imma state, which includes a large number of orbital-modulated (OM) regions with an average size of about 10 nm. The feature of such regions is that the orbital modulation has an incommensurate periodicity and a charge modulation is absent in them. On the other hand, the CE-type state having the commensurate orbital and charge modulations was also confirmed to be present for x = 0.50. In addition to these two states, the state around 100 K for x = 0.46 was found to be characterized by the coexistence state consisting of the C-type orbital-ordered state and the Imma states including OM regions. In other words, the presence of the A-type orbital-ordered state could not be confirmed in the temperature range between 300 K and about 100 K for 0.46 ≤ x ≤ 0.50 in this study.

Crystallographic Features of the State Appearing in the Multiferroic Material Bi&lt;sub&gt;1-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;La&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;FeO&lt;sub&gt;3&lt;/sub&gt; around &lt;i&gt;x&lt;/i&gt; = 0.20

The simple-perovskite system Bi1-xLaxFeO3 (BLFO) is one of mixed-oxide systems having the multiferroic BiFeO3 as an end material, which shows the ferroelectric and antiferromagnetic orders in its ground state. Because of the paraelectric nature of LaFeO3 as another end material, the ferroelectric-to-paraelectric state change can be expected to occur in the mixed-oxide system BLFO. The interesting feature of BLFO is that there are both the PbZrO3-type and incommensurately modulated (IM) states in the intermediate La-content range between the ferroelectric-R3c and paraelectric-Pnma states. Although the detailed features of these two states have not been understood sufficiently, in this study, we focus on the IM state around x = 0.20, and have investigated the crystallographic features of prepared BLFO samples with 0.15 ≤ x ≤ 0.35, mainly by transmission electron microscopy. It was found that six kinds of superlattice reflections were, for instance, present in the reciprocal lattice of the state at 300 K for x = 0.20, in addition to fundamental reflections due to the cubic simple-perovskite structure. To understand the appearance of these superlattice reflections, we regarded the state as a modulated-structure state in this study. Concretely, the modulated structure was assumed to be characterized by the appearance of both the incommensurate wave with qI = &lt;1/(4+δ) 1/(4+δ) 0&gt;c and the commensurate wave with qII = &lt;1/4 0 0&gt;c in the normal-Imma structure. In addition, the appearance of the two modulation waves could also produce the superlattice reflections at the &lt;1/4 1/4 1/4&gt;c-, &lt;1/2 0 0&gt;c-, and &lt;1/2 1/2 0&gt;c-type positions in the reciprocal lattice. From the comparison with the experimental data obtained in this study, our modulated-structure model seems to be appropriate for the IM state in the vicinity of the PbZrO3-type/IM state boundary.

Crystallographic Features of Electronic States in the Highly-Correlated Electronic System Sr&lt;sub&gt;1-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Sm&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;MnO&lt;sub&gt;3&lt;/sub&gt; around &lt;i&gt;x&lt;/i&gt; = 0.50

The highly-correlated electron system Sr1-xSmxMnO3 (SSMO) with the simple-perovskite structure has been found to exhibit fascinating electronic states accompanying antiferromagnetic and ferromagnetic orderings. It was, in particular, reported that the electronic state for 0.46 ≤ x ≤ 0.54 was characterized by the coexistence state consisting of the A-type antiferromagnetic and ferromagnetic states. However, the features of the coexistence state in this Sm-content range have not been understood yet. We have thus investigated the crystallographic features of prepared SSMO samples with 0.46 ≤ x ≤ 0.55, mainly by transmission electron microscopy. As a result, all prepared SSMO samples were first confirmed to have the orthorhombic-Pnma structure at 300 K. When the temperature was lowered from 300 K, in the case of x=0.47, the disordered-Pnma state was found to be transformed into an orbital-modulated (OM) state accompanying an incommensurate modulation. The notable feature of the OM state is that the state becomes unstable with increasing Sm contents at 100 K. In other words, the OM state was never changed into the CE-type state with the orbital and charge modulations. In addition, no orbital-ordered state for the A-type antiferromagnetic ordering was also found for 0.46 ≤ x ≤ 0.55.