Ionic conductivity and crystal structure of fired crystalline zirconium phosphate completely and half exchanged with some monovalent cations

For LiLi-form, the decomposition of dilithium zirconium phosphate with a layered structure and formation of lithium dizirconium triphosphate and zirconium pyrophosphate was achieved by firing at 600°C or above. For NaNa- and KK-forms, any distinct variations of the external apperance were not confirmed by heat-treatments, while the crystal growth was detected for RbRb- and CsCs-forms fired at 900°C. For half ion-exchanged forms, monovalent cation dizirconium triphosphate was mainly formed on heating up to 600°C or above. The activation energy in ionic conduction decreases with increasing monovalent cation radius. This dependency can be realized by Anderson and Stuart's model based on the classical ideas of ionic crystal theory and elasticity theory. The activation energy for the fully exchanged form is slightly higher than that for the half-exchanged form and the pre-exponential factor in σT=σ₀ exp (-E/kT) for the former is less than that for the latter.     

Crystallization behavior of bulk amorphous Se-Sb-In system

In the present work crystallization behavior of the amorphous Se_90–x Sb₁₀In _x (0 x 15) system has been investigated using Differential Scanning Calorimetry (DSC). The DSC data was taken at different heating rates varying from 1°C/min to 90°C/min. From the heating rate dependence of the crystallization temperature, the activation energy for crystallization has been determined using the Kissinger equation and Matusitas equation for non-isothermal crystallization of materials. The effect of addition of In to the Se-Sb system on the dimensionality of crystal growth has been investigated.     

Formation region of monophase with cubic spinel-type oxides in Mn–Co–Ni ternary system

This study was performed to find the composition area of cubic spinel-type monophase oxides composed of the Mn–Co–Ni ternary system. Starting materials were prepared by mixing Mn, Co, and Ni nitrates then evaporating to dryness. Each starting oxide was fired at 700, 800, 900, 1000, and 1100 °C in air. The regions of cubic spinel monophase (CSM) were confirmed to spread with decreasing firing temperatures. The region of CSM at 1000 °C was seen near the line connecting the points of Mn : Co : Ni = 2 : 4 : 0 and 4.5 : 0 : 1.5. The area at 800 °C spread toward Co and Ni, as compared to the results at 1000 °C. In the region containing more Mn above the area of CSM at 800 °C, the phase had tetragonal spinel or -Mn₂O₃ besides cubic spinel structure. Below this area, the phase contained rock-salt-type crystal besides cubic spinel structure. This tendency at 1000 °C was the same as that at 800 °C.     

Selective,low-temperature synthesis of niobium carbide and a mixed (niobium/tungsten) carbide from metal oxide-polyacrylonitrile composites by carbothermal reduction

Composites of polyacrylonitrile (PAN) with the layered oxides (C₆H₁₃NH₃)Nb₃O₈, (C₈H₁₇NH₃)Nb₃O₈ and -(C₆H₁₃NH₃)NbWO₆ undergo carbothermal reduction in an argon atmosphere at 1000 °C to give the cubic carbides NbC_x and (Nb, W)C_x, respectively. Reduction of the Nb₃O₈/PAN composites to NbC_x proceeds via the formation of tetragonal NbO₂, with no other intermediates being detected. Formation of NbC_x begins at 800 °C but is not complete until 1000 °C. The resultant carbide appears in a highly porous form in admixture with approximately 50% wt/wt amorphous carbon. The carbide content, x, of cubic NbC_x increases with heating time (at 1000 °C) as expected. Values of x ranging from 0.69–0.95 have been observed. The cubic mixed carbide, (Nb, W) C_x, is formed similarly from the -NbWO₆ system via an alkylammonium form in the presence of PAN, although progressive separation into cubic NbC_x and hexagonal WC_x occurs at temperatures above 1000 °C. The -NbWO₆ system does not form a well-defined alkylammonium salt; instead a mixture of -HNbWO₆ with PAN gives rise to a very poorly crystalline (Nb, W) carbide on reduction. In all cases, both a layered oxide and PAN are necessary to form the pure carbides at 1000 °C. The oxide/PAN composites appear to be intimate physical mixtures rather than ordered layered nanocomposites.     

Fluxoid pinning by second phases in a superconducting niobium-zirconium alloy

The effects of second phases on the critical currents of superconducting niobium-zirconium alloys containing a nominal 25 wt % zirconium have been determined by superconducting magnetisation experiments. Heat treatment of annealed and extruded materials in the temperature range 600 to 900° C leads to a cellular decomposition of the high temperature structure into two isostructural phases, one niobium-rich ( _Nb) and the other zirconium rich ( _Zr), with an accompanying increase in critical current (at an average field of 20 kOe) up to twelve times the original value. Heat treatment of quenched tubes at 800 or 900° C produces precipitation on sub-boundaries prior to the cellular reaction, this being accompanied by an increase in critical current to at least thirteen times the original value. In this case, however, prolonged heating leads to a fall in critical current which it is suggested is an overageing effect.     

Hydrothermal precipitation and characterization of nanocrystalline BaTiO3 particles

Crystalline BaTiO₃ powders were precipitated by reacting fine TiO₂ particles with a strongly alkaline solution of Ba(OH)₂ under hydrothermal conditions at 80°C to 240°C. The characteristics of the powders were investigated by X-ray diffraction, transmission electron microscopy, thermal analysis and atomic emission spectroscopy. For a fixed reaction time of 24 hours, the average particle size of BaTiO₃ increased from 50 nm at 90°C to 100 nm at 240°C. At synthesis temperatures below 150°C, the BaTiO₃ particles had a narrow size distribution and were predominantly cubic in structure. Higher synthesis temperatures produced a mixture of the cubic and tetragonal phases in which the concentration of the tetragonal phase increased with increasing temperature. A bimodal distribution of sizes developed for long reaction times (96 h) at the highest synthesis temperature (240°C). Thermal analysis revealed little weight loss on heating the powders to temperatures up to 700°C. The influence of particle size and processing-related hydroxyl defects on the crystal structure of the BaTiO₃ powder is discussed.     

Crystallization process of cubic ZrO2 in calcium acetate solution

Ultrafine powders of cubic ZrO₂ were obtained at about 270° C by heating hydrated amorphous ZrO₂ in greater than 0.2 molal calcium acetate solutions. Ca²⁺ ions played a role as nucleii for crystallization and were introduced into distinct sites of the crystalline phases, that is, substituted for Zr⁴⁺ ions. Mn²⁺ ions produced almost the same effects on the crystallization of ZrO₂·EPR spectra for powder samples containing Mn²⁺ ions apparently showed two types as follows: for tetragonal ZrO₂ with a trace of monoclinic ZrO₂, the central fine structure transitions (M=+1/2–1/2) showed a well-resolved hyperfine structure. In addition to the m=0 transition, forbidden m=±1 transitions were observed. For cubic ZrO₂, the broad underlying response was observed as well as the hyperfine structure composed of six main peaks.     

Anomalous thermal expansion of silver chlorate in the tetragonal and cubic phases

Silver chlorate (AgClO₃) undergoes a phase transition from a tetragonal to a cubic phase at 139° C. The temperature dependence of lattice parameters and the coefficient of thermal expansion in the tetragonal phase between 23° C and 130° C and in the cubic phase between 140° C and 184° C have been investigated. The lattice parameters in the tetragonal phase and the lattice parameter in the cubic phase increase with temperature. In the tetragonal phase the coefficient of expansion ( _c) increases with temperature whereas the coefficient of expansion along a perpendicular direction ( _a) decreases with increasing temperature. In the cubic phase the coefficient of expansion shows a pronounced decrease with increasing temperature. These results have been discussed in the light of the known structure.     

Microstructure evolution and ordering in commercial Mg-PSZ

Sintered commercial ZrO₂-9 mol % MgO (PSZ) alloy was heat-treated at different temperatures in the range 900 to 1400° C. The microstructure was studied using transmission electron microscopy (TEM). The as-sintered material was characterized by either fine tetragonal precipitation in cubic matrix grains, or coarser precipitates which had transformed martensitically to the monoclinic symmetry. The diffuse scattering intensity (DSI) was observed to originate from the cubic lattice, and was correlated with the short-range ordering of the oxygen vacancies present in the cubic matrix. However, by annealing at temperatures below 1100° C for relatively short times, long-range ordering occurred in the cubic matrix. The ordered phase was-Mg₂Zr₅O₁₂ with a rhombohedral symmetry, which belongs to the homologous series of M _n O _2n-2 (M₇O₁₂) defect structures derived from the CaF₂-type structure. The ordering process is characteristic only for the cubic regions between the fine-tetragonal precipitates. This microstructure is considered to be a pseudo-equilibrium state and is related to the limited extent of diffusion.     

Ultrafine microsphere particles of zirconium titanate produced by homogeneous dielectric-tuning coprecipitation

Zirconium titanates are widely used in electrical (common microwave dielectrics) and optical devices as well as in bifunctional catalysis and structural ceramics. In this paper, ultrafine amorphous solid microsphere precursor particles of zirconium titanate (Zr _x Ti_{1 – x} O₂) with possibly tailored intraparticle nanostructure (i.e., nanosized pores) were synthesized by a dielectric-tuning solution coprecipitation method, in which inorganic salts were dissolved in a simple water-alcohol mixture and homogeneous nucleation and growth of particles were then induced by heating at temperatures below 100°C. Near-monodispersed particles were obtained. Particle sizes (nanometers to a few micrometers in diameter) were controlled by adjusting the process parameters such as salt concentration, alcohol-to-water volume ratio, temperature, and heating time. Nanosphere particles were produced with a rapid microwave heating nucleation-control scheme. Transmission electron microscopic analysis of each individual microsphere indicates that uniform nanostructures (a few nanometers in pore size) as well as compositional homogeneity (in terms of the Zr/Ti ratio) have been obtained inside each amorphous microsphere. In situhigh-temperature X-ray diffraction data show that no phase segregation was observed in as-preprared microspheres and the transition from amorphous to the single-crystalline ZrTiO₄phase occurred around 650°C for a composition of Zr/Ti = 1. Interestingly, thermal analysis (DTA/TGA) data indicate that the solution synthesis condition seems to affect the crystallization activation energy and onset temperature, which varies from 530 to 680°C.     

Preparation and electrical properties of monophase cubic spinel,Mn1.5Co0.95Ni0.55O4, derived from rock salt type oxide

The purpose of this study was to prepare a sintered body consisting of monophase cubic spinel type oxide, Mn_1.5Co_0.95Ni_0.55O₄, and to evaluate its electrical properties. It was found that cooling from 1400 to 1000 °C in nitrogen did not affect the preservation of the sintered rock salt type oxide formed at 1400 °C. A crack free sintered body of monophase cubic spinel may be obtained by heat treatment at 1000 °C in air, using a specimen cooled from 1400 °C at a rate of 500 °C min ^–1. A heat treatment time in air at 1000 °C of more than 48 h was required to convert the rock salt type structure into a perfect cubic spinel structure. The electrical conductivity, , of the sintered cubic spinel oxide synthesized in this work was found to be stable at 100 and 200 °C in air and at 100, 200 and 300 °C in nitrogen. The sintered spinel oxide was a p-type semiconductor, based on small polaron hopping conduction. The intrinsic hole concentration, n, was estimated to be constant, with a value of 1.6–1.8×10²⁸m^–3. The mobility, , increased exponentially with increasing annealing temperature in both atmospheres, suggesting that the change in is dependent on .     

Photocatalysis and characterization of the gel-derived TiO2 and P-TiO2 transparent thin films

The gel-derived TiO₂ and P-TiO₂ transparent films coated on fused-SiO₂ substrates were prepared using a spin-coating technique. Effects of phosphorus dopants and calcination temperature on crystal structure, crystallite size, microstructure, light transmittance and photocatalytic activity of the films were investigated. By introducing P atoms to Ti-O framework, the growth of anatase crystallites was hindered and the crystal structure of anatase-TiO₂ could withstand temperature up to 900 °C. The photocatalytic activities of the prepared films were characterized using the characteristic time constant (τ) for the photocatalytic reaction. The titania film with a smaller τ value possesses a higher photocatalytic ability. After exposing to 365-nm UV light for 12 h, the P-TiO₂ films calcined between 600 °C and 900 °C can photocatalytically decomposed ≥ 84 mol% of the methylene blue in water with corresponding τ ≤ 7.1 h, which were better than the pure TiO₂ films prepared at the same calcination temperature.     

Synthesis and structural and optical properties of metastable ZrO2 nanoparticles with intergranular Cr3+/Cr4+ doping and grain surface modification

Nanoparticles of stabilized ZrO₂ in a single cubic (c) phase are obtained with an intergranular doping of 4 to 20 at.% Cr³⁺/Cr⁴⁺ additives by a chemical method using a high energy amorphous precursor with polymer molecules of sucrose and polyvinyl alcohol. In the polymer, the metal cations disperse and rearrange in a specific network structure with local symmetry probably similar to that in c-ZrO₂. On heating at 250 to 800°C in air, the polymer network decomposes and burns out spontaneously (with a strong exothermic peak over 350 to 500°C in thermal analysis) in a refined microstructure in 10 to 20 nm diameter particles of near spherical shape. Those are identified to be of c-ZrO₂ by x-ray diffraction. A modified microstructure of 15 to 30 nm crystallites of dispersed tetragonal (t) and/or monoclinic (m) phases in stabilized c-ZrO₂ develops on a prolong heating at 900 to 1000°C from a polymer precursor for 2 h or longer. Particles in t-ZrO₂ are in acicular shape, as long as 450 nm with aspect ratio 5 to 20, while in the shape of platelets in m-phase in an average 300 nm size. It is found that the Cr³⁺/Cr⁴⁺ additives promote formation of c-ZrO₂ by a controlled decomposition and combustion of precursor in small particles at 250 to 800°C temperature. Part of the additives form a thin amorphous surface layer in individual c-ZrO₂ grains so that it prevents them to grow or transform in the equilibrium m-ZrO₂ bulk structure as long as the temperature lies below 900°C. The x-ray diffraction in light of the optical spectrum reveals that part of the Cr⁴⁺ cations occupy Zr⁴⁺ sites in a distorted c-ZrO₂ lattice.     

Micro-hardness, microstructures and thermal stability of (Ti,Cr,Al,Si)N films deposited by cathodic arc method

(Ti,Cr,Al,Si)N films were deposited by cathodic arc method using TiCrAlSi alloy cathodes. It was found that the microstructures of (Ti,Cr,Al,Si)N were closely related to (Al+Si) content. The crystal structure of (Ti,Cr,Al,Si)N was NaCl-type structure up to the (Al+Si) content of 0.60, where it changed to a hexagonal structure. The maximum hardness of 33 GPa was obtained at the lowest (Al+Si) content of 0.56, still in the cubic structure. The micro-hardness decreased down to 28 GPa as the crystal structure changed from NaCl-type to wurtzite-type.To investigate the thermal stabilities of (Ti,Cr,Al,Si)N, the films were annealed in a vacuum furnace. In Ti_0.20Cr_0.20Al_0.55Si_0.05N with cubic structure, the phase segregation occurred by annealing at over 900 °C, while Ti_0.22Cr_0.22Al_0.44Si_0.12N remained in cubic phase up to 1000 °C. The micro-hardness of Ti_0.20Cr_0.20Al_0.55Si_0.05N increased and that of Ti_0.22Cr_0.22Al_0.44Si_0.12N decreased at 1000 °C. Ti_0.20Cr_0.11Al_0.58Si_0.11N with a cubic and hexagonal mixture phase held its (c,h)-mixture phase up to 1000 °C, while there was an indication of an increase both in micro-hardness and in cubic ratio after annealing.In this paper, the micro-hardness and microstructure of (Ti,Cr,Al,Si)N are discussed as a function of annealing temperature and investigated by X-ray diffraction and electron microscopy.     

Crystallization of leucite as the main phase in glass doped with fluorine anions

The crystallization of a multicomponent glass containing 1.63 wt% of F^– anions was studied. The results show in powder glass with particle sizes less than 0.15 mm, that surface crystallization is dominant, whereby two phases: leucite and dioside are formed. In glass powder or particle size about 0.15 mm, three phases, phlogopite, diopside and leucite, are formed, accompanied by an abrupt decrease in the resistance of the glass to crystallization. If the particle sizes are in the range 0.15 to 0.45 mm, both surface and volume crystallization are significant, while with particle sizes >0.45 mm, volume crystallization is dominant. Two nucleation temperatures, T _n1 = 655°C and T _n2 = 675°C, were determined in the temperature range of 600–710°C. These temperatures satisfy the condition that T _n T _g . Crystallization of bulk glass occurs in the temperature range of T _c = 870–1100°C, the crystal phases appearing in the sequence: phlogopite, followed by diopside, followed by leucite. Kinetical and microstructural studies show that the crystallization process is controlled by volume diffusion.     

Decomposition of β-phase in the Heusler alloy Cu2.00Mn1.00Al1.00

Polycrystalline homogenized specimens of the alloy Cu_2.00Mn_1.00Al_1.00 were annealed at temperatures of 360° C, 460° C and 560° C, quenched in water and investigated by means of X-ray diffraction and magnetometry. It was indicated that the process of the decomposition of the-phase of the system Cu-Mn-Al is different at each of the above temperatures. The investigations showed the occurrence of the additional precipitation in the partially decomposed alloy when it was annealed at 200° C.     

Study of the system FePO4-FeVO4 prepared from the solution

The samples of the pseudobinary system (FePO₄)_1–x -(FeVO₄) _x with x=0–1 were prepared by precipitation from a solution of iron nitrate and ammonium phosphate/vanadate, and the evolution of their structure during the heating of the precipitate within the temperature range of 20–1000 °C was studied by thermal analysis, X-ray diffraction and infrared spectroscopy. The samples dried at 120°C were amorphous having a high specific surface area of 160–222 m²g^–1 and their crystallization took place at 440–560 °C. The regions of solid solutions between the two boundary phases were smaller than 10 mol % of the second phase and a new crystalline phase was formed in the system at the composition of FePO₄FeVO₄=11.     

Preparation of Submicron Strontium Sodium Zirconate Powder in Alkaline Solutions

Fine-particle (Sr,Na)ZrO₃ was prepared by boiling a suspension of zirconium and strontium hydroxides in concentrated NaOH and was characterized by powder x-ray diffraction, thermogravimetry, IR spectroscopy, scanning electron microscopy, and x-ray microanalysis. Its structure was refined by the Rietveld method. (Sr,Na)ZrO₃ has an orthorhombically distorted perovskite (ABO₃) structure, with the Sr²⁺ and Na⁺ ions in the A site and Zr⁴⁺ in the B site. The relative A- and B-site occupancies are 100 and 79%, respectively. The cation deficiency is compensated by OH groups, which contain about one-third of the oxygens. In the range 100–900°C, (Sr,Na)ZrO₃ loses water but retains the perovskite structure (with reduced lattice parameters). The synthesized powder consists of 40-nm particles, which form micron-sized spherical aggregates. The aggregates retain their shape during annealing at temperatures of up to 1000°C.     

Crystallization and sinterability of cordierite-based glass powders containing CeO2

Dense glass-ceramics for low firing temperature substrates were prepared by the addition of CeO₂ flux to a glass of the MgO-Al₂O₃-SiO₂ system. The glass powders were fabricated by melting at 1500°C and ball milling. Glass powder compacts prepared by dry pressing were heated at 800–1000°C for 0.5–4 h and sintered at 900–1000°C for 3 h. The crystallization behaviour and sinterability of the glass powder compacts were analysed by thermal and thermomechanical techniques. X-ray diffractometry and scanning electron microscopy. The addition of CeO₂ prevents the formation of -cordierite phase in the glass-ceramics and improves the formation of -cordierite phase. The activation energy of the glass containing CeO₂ for crystallization was lower than that of the CeO₂-free glass. Therefore, crystallization properties were enhanced. Because the crystallization onset temperature increased and the softening temperature decreased on the addition of CeO₂, the sinterability increased and dense glass-ceramics were fabricated below 1000°C. The properties of the glass-ceramics containing CeO₂ appeared to be correct for low firing temperature substrates.     

Sintering and crystallization of mullite powder prepared by sol-gel processing

Mullite powder with the stoichiometric composition (3Al₂O₃.2SiO₂) was synthesized by a sol-gel process, followed by hypercritical drying with CO₂. Within the limits of detection by X-ray diffraction, the powder was amorphous. Crystallization of the powder commenced at 1200 °C and was completed after 1 h at 1350 °C. In situ X-ray analysis showed no intermediate crystalline phases prior to the onset of mullite crystallization and the pattern of the fully crystallized powder was almost identical to that of stoichiometric mullite. The synthesized powder was compacted and sintered to nearly theoretical density below 1250 °C. The microstructure of the sintered sample consisted of nearly equiaxial grains with an average size of 0.2 m. The effect of heating rate (1–15 °C min^–1) on the sintering of the compacted powder was investigated. The sintering rate increased with increasing heating rate, and the maximum in the sintering curve shifted to higher temperatures. The sintering kinetics below 1150 °C can be described by available models for viscous sintering.