Accommodation of non-stoichiometry in TiN<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript> and ZrN<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>

Atomic scale computer simulations, based on density functional calculations, are used to investigate the variation of lattice parameter and bulk modulus with nitrogen deficient non-stoichiometry in titanium and zirconium nitrides. Results assuming a simple distribution of nitrogen vacancies best reflect the remarkably small observed changes in lattice parameter over the whole stoichiometry range for both materials. These are facilitated by small charge transfer to the cations immediately surrounding the nitrogen vacancy and small accompanying lattice relaxations. Conversely variations in bulk modulus are considerable but can be correlated, via a simple function, to the change in materials density.     

Study of gel grown mixed crystals of Ba<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>(IO<Subscript>3</Subscript>)<Subscript>4</Subscript>

The growth of mixed crystals of Ba _x Ca_1−x (IO₃)₄ were carried out with simple gel method. The effect of various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of reactants on the growth was studied. Crystals having different morphologies and habits were obtained. The grown crystals were characterized by XRD, FT-IR, EDAX, TGA, DTA and DSC.     

Microstructure and elastic modulus of ceramic Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Na<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>NbO<Subscript>3</Subscript> perovskite solid solutions prepared at 6 GPa

The microstructure of ceramic samples of high-pressure ferroelectric Li _x Na_{1 − x} NbO₃ (x = 0.17, 0.25) perovskite solid solutions has been studied in relation to synthesis temperature and composition. The elastic properties (Young’s modulus) of the high-pressure Li _x Na_{1 − x} NbO₃ (x = 0.125, 0.17, 0.25) solid solutions have been studied for the first time by a contact technique. The results demonstrate that, with increasing sintering temperature, the Young’s modulus of the high-pressure Li _x Na_{1 − x} NbO₃ solid solutions at singular concentration points (x _i = 0.125 and 0.25, Li/Na = 1/7 and 1/3) increases considerably, whereas that of Li_0.17Na_0.83NbO₃ decreases markedly, which seems to be related to the recrystallization behavior of ordered and disordered solid solutions at high pressures.     

The formaldehyde sensitivity of LaFe<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>-based gas sensor

Rare earth oxides LaFe_1-x Zn _x O₃ were synthesized by sol–gel method. The X-ray diffraction patterns (XRD) showed that LaFe_1-x Zn _x O₃oxides are single phase with orthorhombic perovskite structure, they all show p-type semiconducting properties. Among nanocrystalline LaFe_1-x Zn _x O₃ oxides, LaFe_0.77Zn_0.23O₃ exhibits the highest sensitivity of 44.5 to 100 ppm formaldehyde. The optimal working temperature was found to be around 240 °C. Moreover the LaFe_0.77Zn_0.23O₃ exhibites short response and recovery time to 100 ppm formaldehyde. The lattice parameter doesn’t agree with Vegard’s law with the increasing Zn content, and the relative density was 70–80%.     

Potassium ion conducting K<Subscript>1 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>2</Subscript> solid electrolytes

New potassium ion conducting solid electrolytes based on potassium monoferrite have been prepared through partial substitution of the divalent cation Cd²⁺ on the potassium site, and their properties have been investigated. The introduction of cadmium cations sharply increases the electrical conductivity of KFeO₂ over the entire temperature range studied. In addition to the maximum in conductivity at the boundary of the K_{1 − 2x} Cd _x FeO₂ solid solution, there is a maximum at a higher cadmium content (x = 0.30–0.35). The possible origins of this maximum are discussed.     

Pre-exponential factor in<Emphasis Type="Italic">a</Emphasis>-Se<Subscript>75</Subscript>In<Subscript>25-<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

Temperature dependence of d.c. conductivity is studied ina- Se₇₅In_25-x Pb _x thin films wherex is varied from 0–10. From these measurements, the values of the pre-exponential factor (σ₀) and activation energy (ΔE) are calculated for each glassy alloy. An approximate linear dependence of ln σ₀ on AE is observed in this glassy system with good agreement between the expected and calculated σ₀ values using Meyer-Neldel rule. Linear dependence of ln σ₀ on ΔE in case of amorphous materials indicates that the conduction band tails a finite energy distance towards the valence band and Fermi level is controlled by fixed dominant hole levels deeper in the gap.     

Preparation and studies of some thermal,mechanical and optical properties of<Emphasis Type="Italic">x</Emphasis>Al<Subscript>2</Subscript>O<Subscript>3</Subscript>(1 −<Emphasis Type="Italic">x</Emphasis>)NaPO<Subscript>3</Subscript> glass system

Sodium aluminophosphate glasses having compositions of xAl₂O₃(1-x)NaPO3 (x = 0.05-0.2) were prepared using conventional melt-quench technique. Density, glass transition temperature, microhardness (MH), thermal expansion coefficient (TEC) and transmission characteristics were measured as a function of alumina content for different samples. They were found to depend on O/P ratio with pronounced changes taking place for O/P ratio ≥3.5. Density, glass transition temperature and microhardness were found to increase up to 15 mol% of alumina and then they showed a decreasing trend. Thermal expansion coefficient decreased continuously with alumina content. Optical gaps for different glass samples as measured from transmission characteristics were found to be in the range 3.13–3.51 eV. It initially decreased with alumina content up to 15 mol% and then increased. The behaviour was explained on the basis of change in the average aluminum coordination number from six Al(6) to four Al(4) (i.e. Al(OP)₆/Al(OP)₄ ratio) along with the changes in polyhedra linkages in the glass network due to change in O/P ratio.     

Dielectric properties of (1 − <Emphasis Type="Italic">x</Emphasis>)KNbO3 · <Emphasis Type="Italic">x</Emphasis>BiMg<Subscript>2/3</Subscript>Nb<Subscript>1/3</Subscript>O<Subscript>3</Subscript> perovskite solid solutions

(1 − x) KNbO₃ · xBiMg_2/3Nb_1/3O₃ ceramic materials have been prepared by solid-state reactions. The materials with x < 0.3 have been shown to be perovskite solid solutions. Their average lattice parameter increases linearly with x. Like undoped KNbO₃, the solid solutions undergo a low-temperature (rhombohedral → orthorhombic) ferroelectric phase transition. The transition temperature increases almost linearly with x. The dc electrical conductivity of the ceramics exhibits Arrhenius behavior. The activation energy for conduction rises sharply near the phase transition temperature.     

Unusual magnetic and transport properties of the CMR Pr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3−<Emphasis Type="Italic">y</Emphasis></Subscript> system

The substituted nonstoichiometric perovskite Pr_1−x Ca _x MnO_3−y compounds have been synthesized by a standard combustion technique, which show uniphase solid solutions. The all samples of the Pr_1−x Ca _x MnO_3−y system show an orthorhombic crystal system and the cell volumes are decreased with increasing the larger amounts of substituted atoms or the increasing x values. The mixed valence of Mn ions is identified by the XAS (XANES/EXAFS) spectroscopy and the amounts of Mn⁴⁺ ions are determined by an iodometric titration method. Nonstoichiometric chemical formulas of the Pr_1−x Ca _x Mn_1−τ³⁺Mn_τ⁴⁺O_3−y compounds have been obviously formulated. Magnetic properties are investigated by SQUID and thus the Pr_1−x Ca _x MnO_3−y (x = 0.4, 0.6, and 0.8) compounds show the transition from antiferromagnetic state to paramagnetic state. The Pr_1−x Ca _x MnO_3−y (x = 0.0, 0.2, and 1.0) compounds show the transition from ferromagnetic state to paramagnetic state. The facts that Mn⁴⁺ contents play important roles in the magnetic ordering have been found out. The transport properties have been studied by the DC electrical conductivity measurement under magnetic fields of 0 G and 3 kG. Maximum and minimum MR ratios are 1016% of the Pr_0.6Ca_0.4MnO_2.846, and −77.5% of the PrMnO_3.021 compound, respectively.     

A study on electrodeposited Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys

Zn_1−x Fe _x alloys were electrochemically deposited on AISI 4140 steel substrates from sulfate bath. The bath was consisted of 40 g dm⁻³ ZnSO₄·7H₂O, 20–40 g dm⁻³ FeSO₄·7H₂O_, 25 g dm⁻³ Na₃C₆H₅O₇, and 16 g dm⁻³ H₃BO_3. The effect of bath composition on the electrical resistivity, the phase structure, and the corrosion behavior were investigated by the current–voltage measurements versus temperature, the X-ray diffraction (XRD) analysis, the atomic absorption spectrometry analysis, and the polarization measurements, respectively. Iron content was shown to strongly affect the structure, the electrical resistivity and the corrosion stability of Zn–Fe alloys.     

Structural and thermoelectric properties of Zr<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Er<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>NiSn solid solutions

We have studied the electronic and crystal structures and temperature-dependent resistivity and thermopower of Zr_{1 − x} Er _x NiSn (x = 0–0.20) substitutional semiconductor solid solutions (so-called half-Heusler alloys) in the temperature range 80–380 K. Heavily erbium doped semiconductors with the MgAgAs structure are described in terms of an amorphous semiconductor model. The erbium atoms in Zr_{1 − x} Er _x NiSn are shown to act as acceptors. Density of states calculation results for the Zr_{1 − x} Er _x NiSn alloys are consistent with experimental data.     

Studies on a.c. properties of Ca<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> perovskites

A.c. measurements were preformed on bulk samples of Ca_1−x Sr _x TiO₃ (CST) perovskites with x = 0, 0.1 and 0.5 as a function of temperature range 300–450 K and frequency range 10³–10⁵ Hz . The experimental results indicate that the a.c. conductivity σ_a.c.(ω), dielectric constant ε′ and dielectric loss ε′′ depend on the temperature and frequency. The a.c. conductivity as a function of frequency is well described by a power law Aω ^S with s the frequency exponent. The obtained values of s > 1 decrease with increasing temperature. The present results are compared to the principal theories that describe the universal dielectric response (UDR) behavior.     

Effects of Out-of-Plane Disorder in CaFe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>AsF System

We perform oxygen doping experiments in the CaFeAsF and CaFe_0.88Co_0.12AsF compounds. In the parent compound CaFeAsF, partial replacement of F by O leads to an increase of resistivity and a weakening of spin-density wave transition, indicating that the out-of-plane disorder strongly affects the electronic and magnetic properties of the system. In the CaFe_0.88Co_0.12AsF_1−x O _x system, the doping of oxygen leads to the suppression of superconductivity, reflecting the importance of Ca–F layer disorder in this system.     

Electrical properties and positron annihilation study of (Ba<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ho<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)TiO<Subscript>3</Subscript> ceramics

DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba_1−x Ho _x )TiO₃ ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba_1−x Ho _x )TiO₃ is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO₃ by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The local electron density and defect concentration estimated using positron annihilation technique conforms well to the features found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model.     

Thermoelectric power factor of Ti<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>NiSn alloys

Ti_{1 − x} V _x NiSn (x = 0–0.10) substitutional solid solutions have been prepared by doping the intermetallic semiconductor n-TiNiSn (half-Heusler phase) with vanadium, a donor impurity, and their resistivity and thermopower have been measured at temperatures from 80 to 380 K. The results demonstrate that, when doping of TiNiSn causes no type inversion, the thermoelectric power factor of the solid solution markedly exceeds that of the undoped ternary compound.     

Optical properties of (1−<Emphasis Type="Italic">x</Emphasis>)PbZn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>−<Emphasis Type="Italic">x</Emphasis>PbTiO<Subscript>3</Subscript> single crystals

The temperature dependence of the optical transmission and small-angle light scattering with and without applied constant electric field was studied in relaxor single crystals of 0.91PbZn_1/3Nb_2/3O₃-0.09PbTiO₃ (PZN-PT 91/9) and 0.93PbZn_1/3Nb_2/3O₃-0.07PbTiO₃ (PZN-PT 93/7) solid solutions in the region of two phase transitions: (i) from cubic paraelectric to tetragonal ferroelectric phase at T=T _c and (ii) from tetragonal ferroelectric to rhombohedral ferroelectric phase at T=T _rt. In the absence of external electric field, only the phase transition at T _c proceeds in both PZN-PT 91/9 and PZN-PT 93/7 crystals according to a percolation mechanism and is accompanied by the appearance of a sharp maximum in the small-angle light scattering intensity curve. In PZN-PT 93/7 crystals, the application of a relatively weak electric field induces an additional percolation type phase transition at T _rt.     

Ionic Conductivity of Ln<Subscript>2 + <Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>7 − <Emphasis Type="Italic">x</Emphasis>/2</Subscript> (Ln = Sm-Gd) Solid Solutions

The electrical conductivity of Ln_{2 + x} Zr_{2 − x} O_{7 − x/2} (Ln = Sm-Gd) solid solutions prepared from mechanically activated Ln₂O₃ and ZrO₂ is shown to correlate with their structural properties. In the three systems, the x-T regions are determined in which electrical transport is dominated by oxygen-ion conduction. In the Sm₂O₃-ZrO₂ system, ionic conductivities from 5 × 10⁻⁴ to 6 × 10⁻³ S/cm at 740°C are found in Sm_{2 + x} Zr_{2 − x} O_{7 − x/2} with 26.6, 33.3, 35.5, 37, and 40 mol % Sm₂O₃ prepared at 1450, 1530, and 1600°C. Eu_{2 + x} Zr_{2 − x} O_{7 − x/2} and Gd_{2 + x} Zr_{2 − x} O_{7 − x/2} containing 33.3 to 37 mol % Ln₂O₃ have 740°C ionic conductivities of 10⁻³ to ∼7.5 × 10⁻³ and 10⁻³ to 7 × 10⁻³ S/cm, respectively. The activation energy of conduction in Ln_{2 + x} Zr_{2 − x} O_{7 − x/2} (Ln = Sm-Gd), E _a = 0.84–1.04 eV, increases with the atomic number of Ln and x. The highest ionic conductivity is offered by the stoichiometric Ln₂Zr₂O₇ (Ln = Sm-Gd) pyrochlores prepared at 1600°C, owing to the optimal concentration of Ln_Zr + Zr_Ln antistructure pairs (∼5–22%). The grains in the ceramic samples studied range in size from 0.5 to 2 µm.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 975–984.Original Russian Text Copyright © 2005 by Shlyakhtina, Kolbanev, Knotko, Boguslavskii, Stefanovich, Karyagina, Shcherbakova.     

Structural,Superconducting, and Magnetic Properties of Y<Subscript>1- <Emphasis Type="Italic">x</Emphasis></Subscript>Dy<Subscript>x</Subscript>Rh<Emphasis Type="Italic">4</Emphasis>B<Emphasis Type="Italic">4</Emphasis> Borides

Samples with nominal compositions Y_1-x Dy_xRh₄B₄ are prepared by argon-atmosphere arc melting. The phase composition of the samples and the elemental compositions of the individual phases present are determined by x-ray diffraction and electron-probe x-ray microanalysis. The results indicate that increasing the dysprosium content of the starting mixture increases the percentage of the magnetic phase and reduces that of the superconducting phase in the samples. The electrical resistivity, magnetic susceptibility, and magnetic moment of the samples are measured between 1.6 and 30 K (magnetic fields of up to 14 T). The magnetic phase present in the samples with 0.2 ≤ × ≤ is shown to undergo ferromagnetic ordering at T _magn ≃ 13–13.5 K. The samples with 0 ≤ × ≤ 0.6 contain a superconducting phase with T _c from 9.1 to 5.0 K. The superconducting and magnetic properties of the Y_0.6Dy_0.4Rh₄B₄ sample are examined in detail.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 676–681.Original Russian Text Copyright © 2005 by Burkhanov, Lachenkov, Kuz’micheva, Kovneristyi, Khlybov, Kostyleva, Tomilin.     

Magnetic ordering in Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Se crystals grown by solid-state recrystallization

Cr _x Hg_{1 − x} crystals grown by solid-state recrystallization have been characterized by electron paramagnetic resonance spectroscopy, transport measurements, and X-ray microanalysis. The results demonstrate that the crystals contain rectangular HgCr₂Se₄ inclusions elongated along one of their axes and irregularly shaped Cr _x Hg_{1 − x} and CrHg inclusions. In the range 77–400 K, the electrical properties of samples cut from different parts of the crystals are typical of semiconductors with a strongly degenerate electron gas.     

Atomistic structure and strain relaxation in Czochralski-grown Si<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> bulk alloys

The local atomistic structure in bulk Si_xGe_1−x alloys in the whole composition range 0 < x < 1 was investigated experimentally and theoretically. By extended X-ray absorption fine structure measurements in Czochralski-grown bulk SiGe crystals it is found that bulk SiGe is a random mixture and that the Ge–Ge, Ge–Si and Si–Si bond lengths maintain distinctly different lengths and vary in a linear fashion as a function of alloy composition across the entire composition range 0 < x < 1, in good agreement with expectations derived from the ab-inito electronic structure calculations. The results indicate that SiGe is a typical disorder material and that the bond lengths and bond angles are distorted with alloy composition in SiGe.