Structural mechanisms of superionic conductivity in M 1−x R x F2+x single crystals

The relationship between the superionic transport in fluorite phases M _{1 ? x} R _x F_{2 + x} (M = Ca, Sr, or Ba; R are rare earth elements) and their defect structure has been analyzed. The superionic conductivity of M _{1 ? x} R _x F_{2 + x} crystals is provided by the high concentration of charge carriers. However, the carrier concentration is several tens of times lower than the concentration of anionic defects, which is explained by the presence of defect regions (DRs), which partially block carriers. The dependence of the superionic conductivity of M _{1 ? x} R _x F_{2 + x} phases on the RF₃(x) content has a percolation nature. Crystals of these phases are divided into two groups with respect to the percolation threshold: x _{p, 1} = 2–3 mol % RF₃ and x _{p, 2} = 7–8 mol % RF₃. The corresponding DR volumes are 3000–4000 ų (x _{p, 1}) and 500–700 ų (x _{p, 2}). The x _{p, 1}, and x _{p, 2} values correlate, respectively, with the octahedral cubic {M _{14 ? p} R _p F_{68 ? 69}} and tetrahedral {M _{4 ? p} R _p F₂₆} clusters, which are DR cores. The DR model and cluster structure are indicative of the heterogeneity of nonstoichiometric M _{1 ? x} R _x F_{2 + x} crystals at the nanoscale level with respect to the chemical composition and the electrical and crystallochemical (coordinations of M and R) characteristics.     

Nanostructured crystals of fluorite phases Sr1 − x R x F2 + x and their ordering: 9. The defect crystal and real structure of quenched fluorite phases Sr1 − x Ce x F2 + x (x = 0–0.5)

A Sr_0.7Ce_0.3F_2.3 crystal (CaF₂ type, sp. gr. $Fm\bar 3m$ ), obtained by quenching from melt, has been studied for the first time by X-ray diffraction. Fluorine vacancies and interstitial anions are found in the 8c and 32f sites, respectively. The defect ratio in the Sr_0.7Ce_0.3F_2.3 structure corresponds to the tetrahedral cluster configuration of defects {Sr_{4 ? n} Ce _n F₂₆}. The defect structure of quenched (at a rate of ～25 K/min) crystal differs from that of a crystal grown from melt (cooling at a rate of ～3 K/min) by the displacement of some cations (presumably Ce³⁺) along the threefold axis to the 32f site and the anisotropy of thermal vibrations of ions in the cluster core (F _int(32f)3). The concentration dependence of the lattice parameters of quenched Sr_{1 ? x} Ce _x F_{2 + x} phases (x = 0–0.5) is described by a third-order polynomial: a = 5.80009 + 1.166518 × 10^?3 x ? 1.124969 × 10^?5 x ² + 8.258155 × 10^?8 x ³. The compositional dependence of microdistortions is also nonlinear; maximum microdistortions are observed in the SrF₂ crystal. They decrease with an increase in the cerium concentration x to ～ 0.35. The minimum in the range x = 0.30–0.35 correlates with a composition corresponding to the peak (at x ～ 0.29) in the melting curves of the fluorite phase estimated from the phase diagram of the SrF₂-CeF₃ system (the method of thermal analysis).     

Synthesis and Structure Refinement of Polycrystalline Solid Solution: Na1 + x Zr2 − x Sb x P3O12 (x = 0.1)

Abstract  The solid solution of Na_1 + x Zr_2 − x Sb _x P₃O₁₂ (x = 0.1) was prepared at 1,000 °C by ceramic route. The ceramic material belonging to sodium zirconium phosphate (hereafter NZP) family crystallizes in space group R-3c with unit cell parameters: a = b = 8.77283(16) ?, c = 22.8375(7) ?, α = β = 90.0° γ = 120.0° and Z = 6. The structure of the title phase has been determined by Rietveld refinement of the powder diffraction data on GSAS software. The refinement converges to a satisfactory structure fit with R _p = 0.0764, R _wp = 0.1099 and RF ² = 0.0450. The interatomic distances and bond angles are in good agreement with their standard values. The particle size along prominent reflecting planes ranges between 13 and 50 nm. The polyhedral (ZrO₆ and PO₄ and NaO₈) distortions and valence calculations from bond strength data are also reported. The investigations show that the Sb⁺³ cation occupies the zirconium (A^VI) site of NZP structural framework and resultant charge compensation takes place through partial occupation of M₂ site by Na⁺ ions. Index Abstract  Synthesis and Structure Refinement of Polycrystalline Solid Solution: Na_1 + x Zr _2 −  x Sb _x P ₃ O ₁₂ ( x  = 0.1) O. P. Shrivastava and Rashmi Chourasia Antimony enters crystallochemically in the framework of nano ceramic sodium zirconium phosphate at the Zr site of the ZrO₆ octahedra which are inter linked by PO₄ tetrahedra through corner sharing of the vertical columns. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Nanostructured crystals of fluorite phases Sr1 − x R x F2 + x (R are rare earth elements) and their ordering: 5. A study of the ionic conductivity of as-grown Sr1 − x R x F2 + x crystals

Crystallography Reports - The ionic conductivity σ of Sr1 ? x R x F2 + x crystals (R = Y, La-Lu) has been measured in the temperature range of 324–933 K. The isomorphic...     

Crystal structure of α‴-(Zn1−x Cd x )3As2 (x = 0.26)

Single crystals of the α?-phase of (Zn_{1 ? x} Cd _x )₃As₂ solid solution (x = 0.26) have been prepared and investigated by X-ray diffraction analysis. The tetragonal unit-cell parameters are found to be a = b = 8.5377(2) Å, c = 24.0666(9) Å, sp. gr. I4₁/amd, Z = 16. Zn and Cd atoms in the crystal statistically occupy three symmetrically independent positions in the mirror planes and are tetrahedrally coordinated by arsenic atoms. (Zn,Cd) tetrahedra share edges to form a three-dimensional structure framework. The α?-phase is geometrically related to the fluorite structure. The character of arrangement of tetrahedral vacancies in fluorite-like unit cells is revealed. Chains of tetrahedral vacancies form microchannels oriented parallel the a and b axes, which pierce the three-dimensional structure framework at different levels along the c axis. The structure of α″-Cd₃As₂ crystals is found to be similar to that of α?-(Zn_0.74Cd_0.26)₃As₂.     

X-ray diffraction study of the crystallographic characteristics of TlInS x Se2 − x solid solutions

Crystallographic parameters of TlInS _x Se_{2 ? x} solid solutions have been measured by X-ray diffraction. Dependences of the unit-cell parameters on the composition are determined. It is established that the values of parameters a, b, and c and the angle β decrease with an increase in x. It is shown that the TlInS _x Se_{2 ? x} system includes a continuous series of solid solutions based on the TlInSe₂ compound with tetragonal symmetry at x values ≤ 0.4, while at x ≥ 0.6 solid solutions based on the TlInS₂ compound with a monoclinic structure are formed.     

Local lattice strains in the system of cubic Zn0.999Fe0.001S x Se1 − x (0 ≤ x ≤ 1) crystals

The structure of cubic Zn_0.999Fe_0.001S _x Se_{1 ? x} (0 ≤ x ≤ 1) crystals obtained by vapor-phase chemical transport has been investigated by thermal-neutron diffraction. The diffraction patterns of these crystals are found to exhibit previously unknown diffuse-scattering effects related to local static atomic displacements in the metastable fcc lattice. It is substantiated that the tendency to form polytypes, which is characteristic to a greater extent of zinc sulfide, can be a key factor of instability in the lattice of compounds belonging to the series of anion-substituted solid solutions under study.     

Growth and structure of photosensitive Pb1−x Mn x Te(Ga) epitaxial films

The growth and structure of (1-1.5)-μm-thick Pb_1?x Mn _x Te(Ga)(x = 0.06) films with 0.4?0.9 at % of gallium, grown on BaF₂(111) and Pb_1?x Sn _x Te (x = 0.2) (100) substrates by molecular beam epitaxy, have been investigated. It is established that the films are crystallized into an fcc structure, and their growth planes are (111) and (100), according to the substrate orientation. The optimal conditions for obtaining high-resistivity photosensitive p-and n-type films with a perfect crystal structure (W _1/2 = 80″?100″) have been determined.     

Growth of Ga x In1 − x Sb solid solution single crystals by the Czochralski method

Crystallography Reports - Ga x In1 ? x Sb solid solution single crystals (x = 0.03–0.09) have been grown. The dislocation density and electrophysical parameters are measured. A...     

Concentration dependences of the unit-cell parameters of nonstoichiometric fluorite-type Na0.5 − x R 0.5 + x F2 + 2x phases (R = rare-earth elements)

Unit-cell parameter a of the cubic phases with a varying composition Na_{0.5 ? x} R _{0.5 + x} F_{2 + 2x} (R = Gd-Lu and Y) and with a fluorite-type structure, is described within an accuracy of ±0.003 Å, by the formula a = 4.454 + 0.874r ₃ + x(6.7238r ₃ ? 7.259) where r ₃ is the Shannon “crystal ionic radius” R ³⁺ at c.n. = 8.     

Crystal structure of new synthetic Ca,Na carbonate-borate Ca2Na(Na x Ca0.5 ? x )[B 3 t B 2 δ O8(OH)(O1 ? x OH x )](CO3)

New Ca,Na carbonate-borate Ca₂Na(Na _x Ca_{0.5 ? x} ) [B ₃ ^t B ₂ ^?? O₈(OH)(O_{1 ? x} OH _x )](CO₃) crystals (x ?? 0.4) have been synthesized by the hydrothermal method in the Ca(OH)₂-H₃BO₃-Na₂CO₃-NaCl-system at t = 250°C and P = 70?C80 atm; the structure parameters are found to be a = 11.1848(3) ?, b = 6.4727(2) ?, c = 25.8181(7) ?, ?? = 96.364(3)°, V = 1857.60(9) ?³, sp. gr. C2/c, Z = 8, and ??_calcd = 2.801 g/cm³ (Xcalibur S autodiffractometer (CCD), 2663 reflections with I > 2?? (I), direct solution, refinement by the least-squares method in the anisotropic approximation of thermal atomic vibrations, hydrogen localization, R ₁ = 0.0387). The structure is based on boron-oxygen layers of pentaborate radicals 5(2?? + 3T). Ca and Na polyhedra and CO₃ triangles are located between the layers. A crystallochemical analysis of the new Ca,Na carbonate-borate has established its similarity to natural Na,Ca pentaborates (heidornite and tuzlaite) and synthetic Na,Ba-decaborate.     

Thermal conductivity of single crystals of Ba1–x R x F2 + x (R = La,Ce, Nd,or Gd) solid solutions

The thermal conductivity of single crystals of Ba_1–х R _х F_{2 + х} (R = La, Ce, Nd, or Gd) solid solutions has been experimentally investigated in the temperature range of 50–300 K. With an increase in the content of rare-earth elements, the thermal-conductivity behavior in these series changes from that characteristic of defect single crystals to the behavior typical of glasslike materials. The thermal-conductivity concentration dependences are almost identical, which can be explained by the same type of defect clusters arising upon heterovalent ion substitution.

     

CaCu_3Ti_(4+x)O_(12+2x)陶瓷的电学性能

采用传统的固相合成方法在1100℃,保温3 h制备了不同Ti含量的CaCu3Ti4+xO12+2x陶瓷(x=-0.5,-0.2,0,0.2,0.5)。通过XRD分析了CCTO的相组成;在-20~100℃温度范围内、500 Hz~1 MHz的频率范围测量了CaCu3Ti4+xO12+2x陶瓷的介电特性和阻抗特性。Ti的化学计量变化明显的影响了CCTO陶瓷的电学性能,系统对比发现Ti的含量偏离CaCu3Ti4O12的化学计量比,会显著的降低CCTO陶瓷的介电常数,同时增加介电损耗。     

Photo-acoustic spectroscopy of SixSe1−x glasses

The optical properties near the fundamental absorption edge has been studied for a series of Si_xSe_1−x glasses using photoacoustic spectroscopy. The compositional dependence of the bandgap E_O, derived from these measurements, is presented and contrasted with the GeSe and the SiS systems. This data is qualitatively explained with a model which accounts for differing numbers of homopolar and heteropolar and heteropolar bonds as the composition is varied. Additional support for this interpretation is found in the compositional behavior of the glass transitions of these alloys.     

Nanostructured crystals of fluorite phases Sr1−x R x F2+x and their ordering: VIII. Imperfect crystal structure of Sr0.71Ce0.29F2.29

A congruently melting single crystal of nonstoichiometric phase Sr_0.71Ce_0.29F_2.29 crystallizing into the CaF₂ structural type (sp. gr Fm $\bar 3$ m) has been studied by X-ray diffraction analysis. Vacancies in the main fluorine position 8c and interstitial anions in two 32f positions have been found. The ratio of the structural defects in the Sr_0.71Ce_0.29F_2.29 solid solution corresponds to the tetrahedral configuration of the defect cluster {Sr_{4 ? n} Ce _n F₂₆}.     

Magnetic, magnetocaloric, and lattice properties of the La(Fe x Si1 − x )13 ferromagnets

The magnetic and lattice properties of a sample of La(Fe_0.86Si_0.14)₁₃ ferromagnet have been measured. The influence that neutron irradiation has on the physical properties of this ferromagnet is studied. It is shown that the irradiation of this sample by a fluence of 3 × 10¹⁹ n/cm² increases the lattice constant a and the Curie temperature (T _C ) as the volume magnetostriction decreases. A model of ferromagnet is proposed which satisfactorily describes the dependence a(T) of the initial and irradiated samples and their magnetic properties. The temperature dependence of the change in entropy when switching the magnetic field on and off is calculated. It is established that the change in both the magnetic and lattice parts of the total entropy at the magnetic phase transition must be taken into account for La(Fe _x Si_{1 ? x} )₁₃ compounds.     

Structure and properties of ceramic solid solutions Li x Na1 − x Ta y Nb 1 − y O3 (x = 0–0.05, y = 0–0.04)

The structure of Li_0.03Na_0.97Ta _y Nb_{1 ? y} O₃ ceramic solid solutions and the processes of its disordering with a change in composition and temperature have been studied by full-profile X-ray diffraction analysis and Raman spectroscopy. It was established that at room temperature the structure of Li_0.03Na_0.97Ta_0.05Nb_0.95O₃ solid solutions is close to the NaNbO₃ structure and has a space group P21ma with four formula units per unit cell. It was shown that the oxygen octahedra in the Li _x Na_1?x Ta_0.1Nb_0.9O₃ solid solutions (0, 0.15, 0.03, 0.04, 0.05) are slightly distorted and their geometry is identical to that of octahedra in the NaNbO₃ structure. The temperature dependence of the intensities of lines in the Raman spectrum of Li_0.03Na_0.97Ta_0.4Nb_0.6O₃ solid solutions corresponding to vibrations of Li⁺ and Na⁺ cations in the cuboctahedral structural voids revealed a strong disordering in the alkali metal sublattice at a temperature above 322°C. This may indicate the essential stepwise increase in the Li⁺ cation mobility and may result in a change in the kinetic and energetic characteristics of ion charge transport.     

Bias-induced changes in carrier type of Pb(1−x)Fe(x)S nanocrystalline solution grown thin films

Change of majority carrier type was achieved in nanocrystalline Pb_(1−x)Fe_(x)S thin films by applying a DC-bias on the substrate during their growth by solution growth technique. Critical control of biasing and pH of the solution bath are observed to be necessary to achieve this change. The DC-bias results in slight change in relative concentrations of the constituents in the films, which lead to change in majority carriers without any measurable change in lattice parameter. This modification to the conventional solution growth technique provides the possibility to grow abrupt homojunctions in the nanocrystalline films by sudden change in DC-biasing during film growth.