Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Temporal Stability of Magnetization of ε-In<Subscript>0.24</Subscript>Fe<Subscript>1.76</Subscript>O<Subscript>3</Subscript> Nanoparticles

The kinetics of spontaneous demagnetization in nanoparticles of the exotic epsilon-phase of indium-doped iron(III) oxide (ε-In_0.24Fe_1.76O₃) has been studied using the method of accelerated testing of magnets for temporal stability in a magnetization-reversal field. Time dependences of the magnetization of nanoparticles measured in a wide range of magnetic fields exhibited rectification in semilogarithmic coordinates. The dependence of the magnetic viscosity on the magnetic field has been measured and used for determining the fluctuation field and activation volume. A relationship between the magnetic viscosity and magnetic noise caused by random thermoinduced magnetization reversal in separate nanoparticles is established.     

Growth of bulk β-BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> crystals of high optical quality in the BaB<Subscript>2</Subscript>O<Subscript>4</Subscript>-NaBaBO<Subscript>3</Subscript> system

Phase equilibria along the BaB₂O₄-NaBaBO₃ join of the BaO-B 2 O 3 -Na 2 O system are studied by differential thermal analysis and modified visual thermal analysis. The join is shown to be suitable for growing - BaB₂O₄ crystal of high optical quality.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 64–69. Original Russian Text Copyright © 2005 by Kokh, Kononova, Fedorov, Bekker, Kuznetsov.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.     

Effect of Gd-doping on thermoelectric properties of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9+δ</Subscript> ceramics

A series of Ca_3−x Gd _x Co₄O_9+δ precursor powders were synthesized by the polyacrylamide gel method, and their ceramics were obtained by the Spark Plasma Sintering (SPS). There were lots of defects in the sheet-like grains from SEM and TEM observations. The electrical and the thermal transport properties were obviously affected by the material microstructure. The small polaron hopping conduction mechanism was determined above 600 K, and the hopping activation energy increased with the increase of doping contents. It was found that the Seebeck coefficient and the resistivity of doped samples were markly enhanced due to the impurity compensation effect, and their thermal conductivities were decreased due to the defects scattering. The maximum figure of merit of ZT = 0.24 at 973 K was obtained for Ca_2.7Gd_0.3Co₄O_9+δ.     

Investigation on the synthesis of (Zn<Subscript>1−x</Subscript>Mg<Subscript>x</Subscript>)TiO<Subscript>3</Subscript> and the modulation effect of CaTiO<Subscript>3</Subscript>

(Zn_1−xMg_x)TiO₃ (x = 0.1–0.5) solid solutions were synthesized by solid-state reaction using ZnO, (MgCO₃)₄·Mg(OH)₂·5H₂O and TiO₂ as raw materials. The influences of Zn: Mg ratio and calcining temperature on the properties of (Zn_1−xMg_x)TiO₃ were studied. By adding CaTiO₃ into (Zn_1−xMg_x)TiO₃, the microwave properties and sintering behavior were improved. The ceramics could be sintered at 1150 °C, and the ceramics with excellent microwave properties of τ_f ≈ ±10 ppm/°C, ε ≈ 24, Q × f > 45000 GHz (8 GHz) were obtained.     

Microstructure and properties of the Ba<Subscript>0.75−x</Subscript>Ca<Subscript>x</Subscript>La<Subscript>0.25</Subscript>Fe<Subscript>11.6</Subscript>Co<Subscript>0.25</Subscript>Ti<Subscript>0.15</Subscript>O<Subscript>19</Subscript> hexaferrites

In the case of Ti⁴⁺ remain unchanged, the Ca²⁺ substituted Ba_0.75?xCa_xLa_0.25Fe_11.6Co_0.25Ti_0.15O₁₉ (0?≤?x?≤?0.05) were prepared by conventional solid-state reaction method at temperature of 1280 °C. A ball-to-power weight ratio of 10:1. Their crystal structure and magnetic properties were mainly investigated. The results show that the single magnetoplumbite phase structure transformed into the multiphase structure. Meanwhile, the small amount of α-Fe₂O₃ phase existed in M-type phase. The micrographs were observed by a field emission scanning electron microscopy (SEM). Vibrating sample magnetometer (VSM) was used to analyze the magnetic properties. The saturation magnetization (M _s ) first increases then decreases when x from 0 to 0.03. But, when x from 0.03 to 0.05, the saturation magnetization (M _s ) first increases then decreases too. The maximum value is at x?=?0.04 (M _s ?=?70.73 emu/g). The value of coercivity (H _c ) first increases then decreases when x from 0 to 0.04. But, the value increased when x from 0.04 to 0.05. The maximum value is at x?=?0.02 (H _c ?=?1691 Oe).     

Kinetics of Thermal Transformation of Mg<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 8H<Subscript>2</Subscript>O to Mg<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The kinetics of thermal dehydration of Mg₃(PO₄)₂ · 8H₂O was investigated using thermogravimetry at four different heating rates. The activation energies of the dehydration step of Mg₃(PO₄)₂ · 8H₂O were calculated through the isoconversional Ozawa and Kissinger-Akahira-Sunose (KAS) methods and iterative methods, which were found to be consistent and indicate a single mechanism. The possible conversion function of the dehydration reaction for Mg₃(PO₄)₂ · 8H₂O has been estimated through the Coats and Redfern integral equation, and a better kinetic model such as random nucleation of the “Avrami–Erofeev equation (A _3/2 model)” was found. The thermodynamic functions (ΔH*, ΔG*, and ΔS*) of the dehydration reaction are calculated by the activated complex theory and indicate that it is a non-spontaneous process when the introduction of heat is not connected.     

Characterization of microstructure and properties of Al–Al<Subscript>3</Subscript>Zr–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite

Aluminium-based metal matrix composite strengthened by in situ Al₂O₃ and Al₃Zr particles were synthesized by powder metallurgy route. Phase analysis by X-ray diffraction and scanning electron microscopy revealed that the reaction between Al and ZrO₂ produced Al₂O₃ and Al₃Zr phases in the sintered composites. The hardness of the composite is a strong function of sintering temperature as well as the volume fraction of reinforcements. The dry sliding wear test results clearly indicated that increasing the volume fraction of zirconia particles in the composite improved the wear resistance. Microcutting, ploughing, delamination and oxidation were the main mechanisms of wear.     

Compositional dependence of the structural and dielectric properties of Li<Subscript>2</Subscript>O–GeO<Subscript>2</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

(10Li₂O–20GeO₂–30ZnO–(40-x)Bi₂O₃–xFe₂O₃ where x = 0.0, 3, 6, and 9 mol%) glasses were prepared. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, DC and AC conductivities, and dielectric properties (constant ε′, loss tan δ, AC conductivity, σ _ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of iron ion concentration. The analysis of the results indicate that, the density and molar volume decrease with an increasing of iron content indicates structural changes of the glass matrix. The glass transition temperature T _g and onset of crystallization temperature T _x increase with the variation of concentration of Fe₂O₃ referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter ΔT decrease with increase Fe₂O₃ content, indicates an increasing concentration of iron ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BiO₃, BiO₆, ZnO₄, GeO₄, and GeO₆. The structural changes observed by varying the Fe₂O₃ content in these glasses and evidenced by FTIR investigation suggest that the iron ions play a network modifier role in these glasses while Bi₂O₃, GeO₂, and ZnO play the role of network formers. The temperature dependence of DC and AC conductivities at different frequencies was analyzed using Mott’s small polaron hopping model and, the high temperature activation energies have been estimated and discussed. The dielectric constant and dielectric loss increased with increase in temperature and Fe₂O₃ content.     

Synthesis and study of structural,dielectric, magnetic and magnetoelectric properties of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–CoMn<Subscript>0.2</Subscript>Fe<Subscript>1.8</Subscript>O<Subscript>4</Subscript> composites

Magnetoelectric (ME) composites consisting of K_0.5Na_0.5NbO₃ (KNN) as ferroelectric phase and CoMn_0.2Fe_1.8O₄ (CMFO) as ferrite phase with general formula (x) CoMn_0.2Fe_1.8O₄–(1???x) K_0.5Na_0.5NbO₃ (x?=?10, 20, 30, 40 and 50 wt%) were synthesized using solid state reaction method. X-ray diffraction analysis asserts the existence of component phases including spinel phase of CMFO and orthorhombic phase of KNN. Field emission scanning electron microscopy has been used for studying the morphology and calculation of average grain size. The temperature dependent dielectric properties including dielectric constant (\(\varepsilon ^{\prime}\)) and dielectric loss (tan δ) at different frequencies has been studied and both are found to increase with incorporation of CMFO. Magnetic hysteresis loops have been measured at temperatures of 300 and 5 K. Variation of magnetization versus temperature has been studied in field cooled and zero field cooled modes. Polarization versus electric field (P–E) hysteresis loops are obtained at room temperature indicating presence of ferroelectric ordering in the composites at room temperature. The remnant polarization (2P_r) and coercive field (2E_c) are found to decrease linearly with incorporation of CMFO. ME voltage coefficient (α_ME) has been measured. The maximum value of α_ME is found to be 5.941 mV/cm-Oe for 10% CMFO–90% KNN bulk composite.     

Enhanced microwave dielectric properties of Ba<Subscript>0.40</Subscript>Sr<Subscript>0.60</Subscript>TiO<Subscript>3</Subscript>–Zr<Subscript>0.80</Subscript>Sn<Subscript>0.20</Subscript>TiO<Subscript>4</Subscript> composite ceramics

The (1−x) Ba_0.40Sr_0.60TiO₃ (BST)−xZr_0.80Sn_0.20TiO₄ (ZST) composite ceramics with x = 10, 20, 30, and 40 wt% were fabricated by conventional solid-state reaction method. With increasing of ZST content, the dielectric constant of composite ceramics was decreased and dielectric loss increases. The effect of ZnO addition to 70 wt% BST–30 wt% ZST composition on the microstructure and dielectric properties was investigated. The improvements in dielectric constant, dielectric loss, and microwave dielectric properties of composite ceramics can be achieved by ZnO addition. The sample with 98 wt% (70 wt% BST–30 wt% ZST)–2 wt%ZnO composition exhibits promising dielectric properties, with dielectric constant, loss tangent and tunability at 4 kV/mm, of 125, 0.0016 and 12%, at 10 kHz and room temperature. At ~2 GHz, it possesses a dielectric constant of 101 and a Q factor of 187, which makes it a good candidate for tunable microwave device applications.     

Structure and properties of CaF<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

FTIR spectroscopy has been employed to investigate the structure of CaF₂–B₂O₃ glasses. It is proposed that CaF₂ partially modifies the borate network forming \textCa _{1 / 2} ²⁺ [\textBO _{3 / 2} \textF] ^- {\text{Ca}}_{ 1 / 2}^{ 2+ } [{\text{BO}}_{ 3 / 2} {\text{F]}}^{ - } units. The rest of CaF₂ is assumed to build an amorphous network formed of CaF₄ tetrahedra. Analysis of density and molar volume revealed that the volume of CaF₄ tetrahedron in the studied glasses is slightly greater than that in the crystalline form. Data of density, molar volume, and electric conductivity have been correlated with the glass structure. As far as the authors know, CaF₂–B₂O₃ glasses are investigated for the first time.     

A physicochemical study of the Sb<Subscript>2</Subscript>Se<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>Se<Subscript>3</Subscript> system

We have studied phase relations in the Sb₂Se₃–Nd₂Se₃ system and mapped out its T–x phase diagram using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements. The system contains one compound, with the composition NdSbSe₃, which melts incongruently at 865 K and crystallizes in orthorhombic symmetry with the following lattice parameters: а = 12.77(1) Å, b = 14.08(1) Å, and c = 5.82(5) Å (Z = 8, ρ_meas = 6.20 g/cm³, ρ_x = 6.38 g/cm³). At room temperature, the Nd₂Se₃ solubility in Sb₂Se₃ is 5 mol % and the Sb₂Se₃ solubility in Nd₂Se₃ is 2.5 mol %. The Sb₂Se₃–Nd₂Se₃ system has a eutectic located at 15 mol % Nd₂Se₃, with a melting point at 755 K. The electrical conductivity and thermoelectric power of the (Sb₂Se₃)_1–x (Nd₂Se₃) _x solid solutions have been measured as functions of temperature.     

Synthesis and study of sodium uranate Na<Subscript>2</Subscript>U<Subscript>2</Subscript>O<Subscript>7</Subscript>·6H<Subscript>2</Subscript>O and of products of its dehydration and thermal decomposition

Previously unknown sodium uranate of the composition Na₂U₂O₇·6H₂O was synthesized by precipitation from solution under hydrothermal conditions at 200°С. The composition and structure of this compound were determined by chemical analysis, X-ray diffraction, IR spectroscopy, and thermal analysis. The dehydration and thermal decomposition of the compound were studied.     

Effect of sintering temperatures on properties of BaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass/silica composites for CBGA package

BaO–B₂O₃–SiO₂–Al₂O₃ (BBSA) glass/silica composites synthesized by solid-state reaction method were developed for CBGA packages, and the effects of sintering temperature (900–950 °C) on the phase transformation, microstructure, thermal, mechanical and electrical properties were investigated. XRD results show that the major phases quartz and cristobalite, and the minor phase BaSi₂O₅ are detected in BBSA composites. Furthermore, it was found that the quartz phase transforms to cristobalite phase at 930–940 °C. The formation of cristobalite phase with higher coefficient of thermal expansion (CTE) led to the increase of CTE value of BBSA composites. However, excessive cristobalite phase content would degrade the mechanical properties and the linearity of thermal expansion of the ceramics. BBSA composites sintered at 920 °C exhibited excellent properties: low dielectric constant and loss (ε_r = 6.2, tanδ = 10^?4 at 1 MHz), high bending strength (179 MPa), high CTE (12.19 ppm/°C) as well as superior linearity of the thermal expansion.     

The effect of Fe contents on the local structure and crystallization behavior of SiO<Subscript>2</Subscript>–CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The glass and glass ceramics containing SiO₂–CaO–Fe₂O₃–P₂O₅ were prepared by sol–gel method. The influence of the Fe contents on the crystallization and local structure of the glass and glass ceramics was systematically investigated. The crystal structure of the glass ceramics was identified by XRD characterization. Hematite phase can be precipitated from the glass matrix in all glass ceramics with various Fe contents, and the crystallographic parameters of hematite were determined by XRD Rietveld refinement. The crystallization kinetics of the glasses was investigated in detail. Relative low activation energies were obtained at low Fe contents. The local structure evolution of the glass and glass ceramics has been studied in-depth by means of FTIR and Mössbauer spectroscopy. Fe element is present both as network former and network modifier which significantly influenced the crystallization activation energies of the glasses. The results of this work may be of great significance for the material design and practical applications of bioactive magnetic glass ceramics for hyperthermia.     

Effect of refractory nitride nanoadditives on the properties of (Bi,Pb)<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10+δ</Subscript>

We have investigated the interaction between (Bi,Pb)₂Sr₂Ca₂Cu₃O_10+δ (Bi-2223) and small additions (0.05–0.3 wt %) of nitride powders (TaN, AlN, HfN, NbN, Si₃N₄, TiN, and ZrN) with a particle size from 0.02 to above 0.5 μm and the effect of these nitrides on the microstructure, phase composition, distribution, and morphology of the resulting second-phase inclusions. The concentration and particle size of the nitrides and sintering conditions are shown to influence the superconducting transition temperature T _c, critical current density j _c, irreversible remanent magnetization, bulk density, and mechanical properties of the Bi-2223/nitride composites.     

Frequency dependence of dielectric properties of CaO–SrO–Li<Subscript>2</Subscript>O–Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

CaO–SrO–Li₂O–Ln₂O₃–TiO₂ ceramics were prepared by solid state reaction method, where Ln₂O₃ consists of equal proportions of Nd₂O₃ and Sm₂O₃. Dielectric properties and crystal structure were investigated with respect to the content of TiO₂. Single phase with an orthorhombic perovskites structure was formed within the composition range of investigation. The frequency dependence of dielectric properties of the present ceramics was extensively investigated. Dielectric constant was less sensitive to frequency. However, dielectric loss and temperature coefficients were both very sensitive to frequency and gradually decreased with increasing frequency, such as the variation was more than ten times between 1 MHz and several GHz. The relationship between the temperature coefficient and dielectric loss was also discussed at different frequencies. And the mechanism of the frequency dependence was discussed in term of the role of Li ions.