New La2/3TiO3 Derivatives: Structure and Impedance Spectroscopy

New phases which arise from inserting Na cations on the vacant A-sites of the compound La_2/3TiO₃ have been obtained, giving rise to the series La_4/3−xNa_3xTi₂O₆ (for x=0.16 and 0.28). These phases adopt a perovskite-type structure as deduced from their characterization by electron microscopy and neutron diffraction. Rietveld analyses show that the symmetry is orthorhombic (S.G. Ibmm). Electrical conductivity was determined by impedance spectroscopy, as a function of temperature. A similar behavior is observed for both samples, which behave as ionic conductors with activation energies of 0.92(3) and 0.92(5) eV, respectively.     

High-Pressure Synthesis and Crystal Structure of B2S3

Two new high-pressure phases of binary boron-sulfur compounds, B₂S₃-II and B₂S₃-III, were synthesized at 3-6.2 GPa. A single crystal of B₂S₃-III was grown and the structure was determined (tetragonal, space group I4₁/a, a=16.086(2) Å, c=30.488(4) Å; V=7888(1) ų, Z=100, R=3.0% and R_w=2.8% for 3047 observed data [I>3.00σ(I)]. The structure of B₂S₃-III consists of two kinds of macrotetrahedra built up from 20 and 34 BS₄-tetrahedra. These macrotetrahedra connect each other to form an interpenetrating zincblende-type structure by sharing BS₄-tetrahedra at the corners of those. B₂S₃-III is anticipated having a rather disordered structure. From the UV-Vis diffuse reflectance spectrum, the optical band gap of B₂S₃-III was estimated to be 3.7 eV.     

Some A6B5O18 cation-deficient perovskites in the BaO-La2O3-TiO2-Nb2O5 system

Some dielectric oxides have been synthesized and characterized in the BaO-La₂O₃-TiO₂-Nb₂O₅ system. Through Rietveld refinement of X-ray powder diffraction data, Ba₅LaTi₂Nb₃O₁₈ and Ba₄La₂Ti₃Nb₂O₁₈ are identified as the A_nB_n−1O_3n (n=6) type cation-deficient perovskites with space group and lattice constants , and for Ba₅LaTi₂Nb₃O₁₈; , and for Ba₄La₂Ti₃Nb₂O₁₈, respectively. Their ceramics exhibit high dielectric constant up to 57 and high quality factors (Qf) up to 21,273 GHz. The temperature coefficient of resonant frequency (τ_f) of these ceramics is decreased with the increase of B-site bond valence.     

An Electron Diffraction and XRPD Study of Superlattice Ordering in the Elpasolite-Related Oxyfluoride K3MoO3F3

A detailed electron diffraction and XRPD study has been made of the room-temperature α polymorph of K₃MoO₃F₃. It is shown that the true symmetry of this polymorph is neither tetragonal, trigonal, nor triclinic as previously reported but rather monoclinic I1a1, a=2a_p−c_p, b=4b_p, c=a_p+2c_p when expressed in terms of the underlying elpasolite (ordered perovskite) parent structure type. A highly structured, three-dimensional, continuous diffuse intensity distribution (presumably arising from local O/F ordering and associated structural relaxation) is shown to coexist with the sharp satellite reflections characteristic of the monoclinic supercell.     

Strained Structure in Ho0.5Sr0.5MnO3

The Ho_0.5Sr_0.5MnO₃ perovskite, synthesized in air, has been studied by combining neutron powder and electron diffraction techniques. The Pnma-type structure exhibits a strong tilting of the MnO₆ octahedra. This octahedra tilting and microtwinning involve a complex strained structure. No structural transition is observed down to 1.4 K, but short-range A-type antiferromagnetism running over only a few perovskite subcells is evidenced below ≈90 K. The different behavior of this perovskite compared to other Ln_0.5Sr_0.5MnO₃ perovskites is discussed in terms of A-site cationic mismatch.     

High-resolution neutron powder diffraction study on the structure of Sr2SnO4

From the high-resolution time-of-flight neutron powder diffraction data, the crystal structure of Sr₂SnO₄ at the temperature range between 4 and 300 K has been investigated. The Rietveld refinement has shown that Sr₂SnO₄ belongs to the space group Pccn, which can be derived from the tetragonal K₂NiF₄ structure by tilting the SnO₆ octahedra along the [100]_T- and [010]_T-axis, respectively, with non-equal tilts. The earlier reported first-order phase transition in Sr₂SnO₄, from Bmab to P4₂/ncm, has not been observed.     

Synthesis, Crystal Structure and Physical Properties of LixMg0.857−xCu2.143O3−y

Solid solutions of Li-doped Mg_0.857Cu_2.143O₃ (Li_xMg_0.857−xCu_2.143O_3−y) were prepared at 950°C for 12 h in air by the solid-state method using Li₂CO₃, MgO and CuO powders. The solid solutions were obtained as the single α phase with the güggenite structure in 0≦x≦0.06 region. With the increasing of the Li content x, the lattice parameters a, b and unit cell volume V decreased, while c increased. On the basis of the charge neutrality, hole carrier estimated by the oxygen content increased with the Li substitution. The Seebeck coefficient at room temperature of x = 0.03 sample was +400 μV/K. The electrical resistivity ρ at room temperature drastically decreased with the increasing x. Temperature dependences of ρ for x = 0.01, 0.03 and 0.06 samples were semi-conductive behavior from room temperature to about 12 K. Interaction between Cu²⁺ and Cu²⁺ through O²⁻ seems to be somewhat large antiferromagnetic one. Sperconducting transition was not detected in the temperature range.     

Structure determination from powder diffraction data and thermal behaviour of layered lead nitrate oxalate hydrate, Pb2(NO3)2(C2O4).2H2O

The mixed lead nitrate oxalate, Pb₂(NO₃)₂(C₂O₄).2H₂O, has been obtained in a polycrystalline form in the course of a study on precursors of nanocrystalline PZT-type oxides. Its crystal structure has been solved from powder diffraction data collected using a monochromatic radiation from a conventional X-ray source. The symmetry is monoclinic, space group P2₁/c (No. 14), the cell dimensions are a=10.623(2) Å, b=7.9559(9) Å, c=6.1932(5) Å, β=104.49(1)° and Z=4. The structure consists of a stacking of complex double sheets parallel to (1 0 0), forming layers held together by hydrogen bonds. The sheets result from the condensation of PbO₁₀ polyhedra, in which the oxalate and nitrate groups, as well as water molecules, play a major role. The structure is discussed in terms of Pb---O distances, polyhedra shape and lead coordination, with emphasis on the dimensional polymerisation role of water molecules. The thermal behaviour of this layered compound is carefully described from temperature-dependent powder diffraction and thermogravimetric measurements. The enthalpy, Δ_rH=232(3) kJ mol⁻¹, and entropy, Δ_rS=532(8) J K⁻¹ mol⁻¹, of the dehydration reaction have been determined. The high value of Δ_rH demonstrates that the water molecules are strongly bonded in the structure. The complex decomposition proceeds through the crystallisation and decomposition of Pb(NO₃)₂(C₂O₄) into Pb(NO₃)₂ and PbC₂O₄, and, finally, various lead oxides.     

Crystal structure of Ca2Ln3Sb3O14 (Ln=La, Pr, Nd and Y): A novel variant of weberite

The crystal structures of Ca₂Ln₃Sb₃O₁₄ (Ln=La, Pr, Nd and Y) and Ca₂Sb₂O₇ at room temperature were refined by the Rietveld method using combined X-ray and neutron powder diffraction data. Ca₂Sb₂O₇ adopts the weberite structure having the space group Imma. The structures of Ca₂Ln₃Sb₃O₁₄ are, however, neither the orthorhombic nor the tetragonal chiolite as has been suggested previously. They crystallize in the monoclinic space group I2/m11 belonging to a hitherto unknown type of deformation of the parent (orthorhombic) weberite structure.     

High-resolution neutron powder diffraction study on the phase transitions in BaPbO3

Phase transitions that occurred in perovskite BaPbO₃ have been investigated using high-resolution time-of-flight neutron powder diffraction. The structure at room temperature is orthorhombic (space group Imma), which is derived from the cubic aristotype by tilting the PbO₆ octahedra around the two-fold axis (tilt system a⁰b⁻b⁻). The orthorhombic structure shows anisotropic line broadening attributed to the presence of micro twins. At above about 573 K, BaPbO₃ undergoes a discontinuous phase transition to a tetragonal structure (space group I4/mcm) with the tilting of the PbO₆ octahedra being about the four-fold axis of the cubic aristotype (tilt system a⁰a⁰c⁻). With further increasing the temperature, BaPbO₃ experiences a continuous phase transition to a simple cubic structure (space group Pm3¯m) at above about 673 K. The later phase transition is characterised by a critical exponent of β=0.36, depicted by the three-dimensional Heisenberg universality class. The earlier reported Imma→I2/m phase transition above room temperature has not been observed.     

Neutron powder diffraction study of phase transitions in Sr2SnO4

The phase transitions in Sr₂SnO₄ at high temperature have been studied using high resolution time-of-flight powder neutron diffraction. The room temperature structure of Sr₂SnO₄ is orthorhombic (Pccn), which can be derived from the tetragonal K₂NiF₄ structure by tilting the SnO₆ octahedra along the tetragonal [100]_T- and [010]_T-axes with non-equal tilts. At the temperature of about 423 K, it transforms to another orthorhombic structure (Bmab) characterized by the SnO₆ octahedral tilt around the [110]_T-axis. At still higher temperatures (∼573 K) the structure was found to be tetragonal K₂NiF₄-type (I4/mmm).     

Crystal structures and phase transitions of Sr2CrSbO6

Sr₂CrSbO₆ was synthesized by the conventional solid-state reaction process. X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) has been used to reinvestigate the structure at room temperature and to study the phase transitions at high- and low-temperature. Rietveld analysis revealed that Sr₂CrSbO₆ crystallizes at room temperature in a monoclinic system having a space group I2/m, with a=5.5574(1) Å; b=5.5782(1) Å; c=7.8506(2) Å and β=90.06(2), no P2₁/n space group as was previously reported. The high-temperature study (300-870 K) has shown that the compound presents the following temperature induced phase-transition sequence: I2/m-I4/m-Fm-3m. The low-temperature study (100-300 K) demonstrated that the room-temperature I2/m monoclinic symmetry seems to be stable down to 100 K.     

Synthesis, Crystal Structure, and Magnetic Properties of Quasi-One-Dimensional Oxides Ca3CuMnO6 and Ca3Co1+xMn1−xO6

Synthesis conditions, crystal structures, and magnetic properties of quasi-one-dimensional complex oxides Ca₃CuMnO₆ (space group P-1, z=4, triclinic cell) and Ca₃Co_1+xMn_1−xO₆ with x=0, 0.25, 1.0 (structural type K₄CdCl₆, space group R-3c, z=6) are presented. The crystal structures of Ca₃CoMnO₆ and Ca₃CuMnO₆ were refined using neutron and combined X-ray and neutron diffraction analysis, respectively. The interatomic distances in oxygen polyhedra were found. In contrast to ferromagnetic Ca₃Co₂O₆ (T_c=24 K), manganese-containing phases Ca₃Co_1+xMn_1−xO₆ are characterized by antiferromagnetic interactions with Neel temperatures 18 K (x=0.25) and 13 K (x=0). For Ca₃CuMnO₆T_N was established to be 6 K.     

钙钛矿ABX3型材料的结构与性质调控

近年来,钙钛矿太阳能电池由于其效率高、制造成本低、工艺简单等特点受到广泛关注,成为目前太阳能电池领域的研究热点。在钙钛矿太阳能电池中,无机-有机杂化ABX₃材料非常重要。它既作为光吸收材料,同时又作为载流子传输材料,因此它的光电性质直接影响到太阳能电池的效率。本文综述了调控钙钛矿型无机有机金属卤化物ABX₃结构和性质的几种途径。     

杂化钙钛矿(NH_3C_6H_(12)NH_3)CuCl_4的制备与表征

采用低温溶液法合成了含有二铵阳离子结构的新型二维层状结构的有机/无机杂化钙钛矿材料(NH_3C_6H_(12)NH_3)CuCl_4。采用元素分析、红外光谱、X射线衍射和紫外-可见光吸收光谱等手段对其结构与性能进行了表征。结果表明该材料的紫外-可见吸收光谱吸收峰位于285 nm和387 nm,层间距为1.18 nm。二铵阳离子的引入,使有机层~+NH_3C_6H_(12)NH_3~+与2个相邻的无机框架Cu Cl42-分别通过较强的氢键结合在一起,排列更为规整,热稳定性更高。与单铵阳离子结构的杂化钙钛矿材料相比,由于不存在两层有机分子层间较弱的范德华力,(NH_3C_6H_(12)NH_3)CuCl_4材料的电阻率为1.36×105Ω·cm,比单胺结构的杂化钙钛矿材料的电阻率低3个数量级。     

杂化钙钛矿(NH3C6H12NH3)CuCl4的制备与表征

采用低温溶液法合成了含有二铵阳离子结构的新型二维层状结构的有机/无机杂化钙钛矿材料（NH₃C₆H₁₂NH₃） CuCl₄。采用元素分析、红外光谱、X射线衍射和紫外-可见光吸收光谱等手段对其结构与性能进行了表征。结果表明该材料的紫外-可见吸收光谱吸收峰位于285 nm和387 nm,层间距为1.18 nm。二铵阳离子的引入,使有机层⁺NH₃C₆H₁₂NH₃+与2个相邻的无机框架CuCl₄^2-分别通过较强的氢键结合在一起,排列更为规整,热稳定性更高。与单铵阳离子结构的杂化钙钛矿材料相比,由于不存在两层有机分子层间较弱的范德华力,（NH₃C₆H₁₂NH₃） CuCl₄材料的电阻率为1.36×10⁵ Ω·cm,比单胺结构的杂化钙钛矿材料的电阻率低3个数量级。     

The Ternary Compounds Pd13ln5.25Sb3.75 and Pdln1.26Sb0.74: Crystal Structure and Electronic Structure Calculations

The new ternary compound Pd₁₃In_5.25Sb_3.75 was found. Its crystal structure was determined using a CCD diffractometer at room temperature. Evaluations and refinements finally yielded a C-centered monoclinic structure (space group, C2/c; Pearson symbol, mC88, Z=4) with a=15.189(2) Å, b=8.799(1) Å, c=13.602(2) Å, and β=123.83(1)°. For the entire data set of 3706 independent reflections residual values are R=0.0461 and R_w=0.0789. The structure was found to be isotypic to Pd₁₃Pb₉ with In and Sb on the Pb sites. The existence of a further ternary compound, which was already described as Pd₃In₄Sb₂, could be confirmed. Its composition range was determined by EPMA to be PdIn_1.2-1.3Sb_0.8-0.7. It does not melt congruently and we were not able to find suitable single crystals. However, we were able to prepare the pure ternary compound in order to perform X-ray powder diffraction using a Guinier image plate technique. The entire diffraction spectrum was refined by full profile Rietveld method using the program Fullprof. The α-PdSn₂ structure type (space group, I4₁/acd; Pearson symbol, t148, Z=16), proposed for this compound, was confirmed and the lattice parameters are a=6.4350(1) Å and c=24.3638(3) Å. The residual values were R_p=5.34 and R_wp=6.70. The tetragonal PdSn₂ structure type is a mixed variant of the CaF₂ type and the CuAl₂ type structure. Also in this ternary compound we assumed a random contribution of In and Sb over the 16e and 16f positions. The electronic structures of both compounds were investigated by extended Hückel calculations. Crystal orbital overlap populations show extended bonding interactions between the main group elements. The bonding interactions of the main group elements are almost optimized at the experimentally observed In/Sb ratio of the ternary compound. The In/Sb ratio in Pd₁₃In_5.25Sb_3.75 can thus be rationalized on the basis of the electronic structure.     

Crystal Structure and Magnetic Properties of a New Iron(III) Silicophosphate Fe3P5SiO19 Studied by Neutron Diffraction and Mössbauer Techniques

Fe₃P₅SiO₁₉ has been prepared by solid state reaction of Fe(PO₃)₃, FePO₄, and SiO₂ at 1000°C. The structure has been determined from a single crystal through direct methods and difference Fourier synthesis and refined to R=0.052. The unit cell is hexagonal, space group P6₃, with a=14.4804(8) Å, c=7.4256(2) Å, and Z=4. The three-dimensional framework is built up from [Fe₂O₉] units of two faces sharing octahedra and Si₂O₇ disilicates linked by PO₄ tetrahedra. Fe₃P₅SiO₁₉ is isotypic with V₃P₅SiO₁₉. Fe₃P₅SiO₁₉ is antiferromagnetic below T_N=35 K. The magnetic structure has been determined by means of powder neutron diffraction methods: the magnetic moments are antiferromagnetically coupled inside the [Fe₂O₉] units, in agreement with the Goodenough rules. These units are linked to each other through several Fe-O-P-O-Fe super-superexchange pathways and form antiferromagnetic [001] rows. The moment direction lies in the (001) plane (μ_Fe=4.56(5) μ_B at 2 K). There is a competition between the intra- and interunits interactions which all are antiferromagnetic and cannot be simultaneously satisfied without frustration. Mössbauer spectra are fitted with two doublets and two sextuplets in the paramagnetic and antiferromagnetic states, respectively. Their rather high isomer shifts are explained by the inductive effect. The magnetic interactions are discussed.