A study of the stabilization of aluminium titanate

A tialite ceramics (Al₂TiO₅) was synthesized at a temperature of 1500 °C, incorporating CaF₂, La₂O₃, SiO₂ or kaolin and MgO additives. Its thermal stability was investigated by thermocycling in a reducing medium. The batches containing SiO₂ or kaolin additives underwent a decomposition to rutile and corundum. A stabilized ceramic with added MgO was produced. X-ray and electron-probe microanalysis established the presence of Mg/Al, Ti_z/O₄, Al_2–x-y Ti_1+x Mg _y O₅ and Ca_1–x La _x /Al_12–y-z Mg _y Ti _z /O₁₉ solid solutions, which retained their chemical composition after thermocycling in a reducing medium.     

Thermal expansion of grain-boundary cracked aluminium titanate ceramics

The relation between thermal expansion coefficient and grain-boundary crack volume of aluminium titanate ceramics has been calculated based on the thermal expansion data of a single crystal. The calculation began with the drawing of a frequency distribution curve of the thermal expansion coefficient for a single grain. Using the single-grain distribution curve, a distribution curve of an average coefficient for two adjacent grains was derived. The thermal expansion with a partially grain-boundary cracked body was calculated in relation to the amount of cracked boundary from the average distribution curves. The expected relation between crack volume and thermal expansion was close to that of the experimental data.     

Thermal cycling of iron- and magnesium-containing aluminium titanate in a dilatometer

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Nitrogen-containing aluminium titanate

In the Ti-Al-O-N system a phase isostructural to aluminium titanate but with expanded unit cell dimensions was observed. It was stable between 1400 and 1700 °C and has unit cell dimensions of a=0.3719 nm, b=0.9703 nm and c=0.9869 nm with a composition of Ti _1.00 ⁴⁺ Al _0.54 ³⁺ Ti _1.46 ³⁺ N _0.28 ^3– O _4.58 ^2– _0.14 Several samples were prepared by reaction sintering mixtures of TiN, Al₂O₃ and AlN powders at 1400 to 1470 °C for 4 h in a nitrogen atmosphere to maximize this phase. One specific advantage of the nitrogen-containing aluminium titanate over aluminium titanate is that the former is unchanged at 1150 °C in a nitrogen atmosphere whereas the latter decomposes. In the Al₂O₃-TiO₂ oxide system Al₂TiO₅ solid solution extends to approximately Al_0.75Ti_2.25O₅ at 1470 °C under the mildly reducing conditions of a graphite furnace. The unit cell volume increases linearly with the increasing replacement of Al³⁺ by Ti³⁺.     

Features of the structure and ferroelectric properties of the solid solutions of lead titanate with rare-earth metals

A secondary periodicity in variation of the properties of ferroelectric solid solutions of lead titanate with rare-earth metals is established. It is demonstrated that this behavior is related both to the modifying cations belonging to two natural subgroups and to the energetic features of their 4f levels. The extrema of the structural and ferroelectric characteristics correspond to the domains of electron instability.     

Thermal properties of liquid and solid metals

New generalized expressions for compressibility and thermal expansion of liquid and solid metals are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 6, pp. 979–983, June, 1986.     

Synthesis and properties of SnTe-PrTe solid solutions

A partial phase diagram of the SnTe-PrTe system has been constructed. The system is shown to contain SnTe-based solid solutions. The electrical conductivity, Hall coefficient, thermoelectric power, and thermal conductivity of the SnTe-PrTe alloys containing 1, 2, and 3 mol % PrTe have been measured as functions of temperature, and their thermoelectric figure of merit has been determined.     

The effects of additives on the properties and structure of hot-pressed aluminium titanate ceramics

The effects of additives (MgO-Al₂O₃-SiO₂, Al₂O₃-SiO₂, Si₃N₄, SiC) on the properties and structure of hot-pressed aluminium titanate ceramics were studied. The results showed that the bending strength of aluminium titanate ceramics with additives was improved greatly, while the thermal expansion coefficient was also increased due to the change of structure for aluminium titanate ceramics. The results of X-ray diffraction patterns showed that a solid state reaction occurred between the additives and aluminium titanate, and a solid solution was formed.     

Luminescent properties of Cd-In-Te solid solutions

The composition dependences of the unit-cell parameter for CdTe-based solid solutions in the CdTe-InTe and CdTe-In₄Te₃ joins have been used to determine the limits of the solid solutions. Magnetic susceptibility data and the measured and X-ray densities of the solid solutions suggest that CdTe doped with In₂Te₂ or In₄Te₃ contains In⁺ and In³⁺ on the cation site. The cathodoluminescence spectra of CdTe doped with In₂Te₂, In₄Te₃, and In₂Te₃ have been measured, and the effect of mixed heterovalent substitution (In⁺ and In³⁺) on the luminescence behavior of CdTe has been analyzed.     

Thermal properties of solid ND3

The heat capacity (2–197 K), thermal expansion (23–160 K), and thermal conductivity (30–120 K) of solid deuteroammonia have been studied, and the enthalpy of fusionH _tr and temperatureT _tr corresponding to the triple point of ND ₃ determined. Comparison is given of the thermal properties of NH ₃ and ND ₃ , and the temperature dependence of the properties studied is discussed.     

Thermal conductivity of binary disordered continuous solid solutions

A simplified model for the structure and an approximate method of computing the thermal conductivity of continuous solid solutions are proposed. The method is suitable for a check, extension of the measurement results, and prediction of the thermal conductivity of solid solutions.     

磷酸铝-聚醚砜层状复合材料的隔热及介电性能

采用高温煅烧成型工艺在聚醚砜(PES)基体表面复合了AlPO4耐热层,制备得到了AlPO4-PES层状复合材料。利用SEM、激光共聚焦显微镜三维形貌分析(CLSM-3D)、FTIR和TGA等分析技术对AlPO4-PES微观结构、化学成分以及热稳定性进行了表征。研究了AlPO4含量对AlPO4-PES层状复合材料的热导率和介电性能的影响。结果表明:AlPO4层显著地改变了PES基体的微观结构,二者之间通过物理方式紧密结合;随着AlPO4含量的增加,AlPO4-PES层状复合材料的热稳定性明显增强,而热导率却不断降低;AlPO4-PES层状复合材料的介电常数和介电损耗均随着AlPO4含量的增加而减小,并且在0.1~5MHz测试范围内表现出良好的频率稳定性。     

Structural and electrical properties of cadmium-sulpho-selenide solid solutions

Complete solid solutions of CdS _x Se_1–x (0x1) were synthesized by vacuum fusion of stoichiometric proportions of CdS and CdSe. X-ray diffraction data revealed that they possess the hexagonal wurtzite structure. The unit cell lattice constants vary linearly with the composition parameter,x, following Vegard's law.Thin films of CdS _x Se_1–x (0x1) solid solutions could be deposited onto glass substrates by thermal evaporation of the bulk material in 10^–4 Pa vacuum. Structural investigation showed that the films are polycrystalline with predominant appearance of the (002) reflecting plane. On annealing at 250°C in 10^–2 Pa vacuum atmosphere, aggregation and rearrangement of the as-deposited tiny crystallite occurred, preserving the same crystal structure.The dark electrical resistivity of the films is independent on the film thickness, but it varies appreciably with the composition parameter,x, showing a minimum resistivity of 0.02 cm atx=0.55. The temperature dependence of the resistivity follows the semiconducting behaviour with an extrinsic and an intrinsic conduction below and above 70°C, respectively. The determined activation energies 0.2 eV and 0.8 eV, respectively, correspond to shallow and deep trap levels, respectively.     

Piezoelectric and dielectric properties of PZN-BT-PZT solid solutions

Pb(Zn_1/3Nb_2/3)O₃ ceramics with the perovskite structure can be stabilized by substituting 6–7 mol % BaTiO₃ (BT). Piezoelectric and dielectric properties of the pseudo-binary system (1–x)(0.94PZN-0.06BT) -xPb(Zr_(1–y)Ti_y)O₃ were studied, and the effects of Zr/Ti ratios and thermal annealing process on the piezoelectric and dielectric properties were also discussed. The results show that the piezoelectric properties of this ceramic system are very good when x is about 0.50 and y is about 0.47 with K_p = 70%, d₃₃=560 pC/N, _m #x2248;23,000. These ceramics are favorable to piezoelectric actuators.     

Long-term thermal stability and mechanical properties of aluminium titanate at 1000–1200°C

Two aluminium titanate (AT) ceramics containing magnesium and iron were sintered to study their high-temperature mechanical property and thermal stability. Both materials exhibited a pronounced inelastic stress–strain behaviour which is caused by extensive microcracks. The microcracking also led to an increasing R-curve behaviour which was measured in the Mg–AT material in the as-sintered state. At 1000 °C, crack healing took place which led to an increase in the strength and Young's modulus. At 1100 °C, the glassy phase started to soften which resulted in a reduction of the strength and Young's modulus. Thermal stability was assessed after annealing at 1000, 1100 and 1200 °C for 250 and 1000 h in air. Although the Fe–AT material did not show any significant decomposition and degradation in mechanical properties, the Mg–AT material annealed at 1000 and 1100 °C showed pronounced decomposition into corundum and rutile. The decomposition led to a brittle fracture, but increased the strength and Young's modulus. Both materials showed a lower coefficient of thermal expansion (<0.2×10-6K-1) than that of stoichiometric aluminium titanate. The results are discussed with respect to the microstructure and phase relationship. © 1998 Chapman & Hall     

Thermal properties of paramagnetic solid helium-3

It was shown in recent work that over a limited molar volume range and at asymptotically high temperatures the thermal modulations of the pressure along isochores of paramagnetic solid³He could be accounted for through the formalism of the Heisenberg model of an antiferromagnetically interacting localized spin-1/2 system. The internal consistency of this formalism requires the characteristic exchange-interaction parameter of the model derived from pressure modulation data to be identical with that appearing in the other thermal properties of this quantum solid. In a restricted temperature region where the spin excitations are the dominant thermal excitations of the solid, heat capacity data yield exchange-interaction parameters in fair agreement with those derived from pressures along isochores of larger molar volume. At higher temperatures, within well-defined limitations, thermal excitations involve both spin and phonon excitations. Here, because of the opposite temperature variations of the spin and phonon heat capacity components, the ensuing heat capacity minimum determines exactly the exchange-energy parameter and the relevant limiting Debye temperature as a function of the measured temperature location and value of the heat capacity extremum along the experimentally explored isochore. The exchange-energy parameters so derived display larger deviations from their predicted pressure-based values than those resulting from the lower temperature but still asymptotic spin-only heat capacities. At the present time, ambiguities in the experimental determinations of the characteristic Weiss temperatures of the asymptotic paramagnetic susceptibilities prevent one from deriving exchange-energy parameters with them. The present work leads to the prediction, within the limitations of the model formalism, of thermal properties of magnetized solid³He. Experimental investigations of these properties offer new approaches for probing the validity of the model formalism applied to paramagnetic solid³He.     

Pyroelectric properties of lead-barium titanate and lead-strontium titanate

Pyroelectric properties of poled solid solutions of lead-barium titanate and leadstrontium titanate have been investigated in the temperature range covering their transition points. The values of pyroelectric current and coefficients of (Pb _x − Ba_{1 −x} )TiO₃ and (Pb _x − Sr_{1 −x} )TiO₃(x = 0·8 − 0·5) show a sharp peak at the Curie temperature. It is observed that these values change with Ba or Sr concentration in the respective solid solutions.