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Abstract  

Studies on thermal expansion of the MNbO4 type phases where M=Al, Cr, Fe, Ga have been carried out in the high-temperature X-ray diffraction attachment. In the case of isotypic AlNbO4 and GaNbO4 compounds the structure of which consists of the ReO3 type blocks, the direction of minimal thermal expansion is consistent with the direction in which these blocks spread to infinity. In the case of CrNbO4, the maximal thermal expansion direction is consistent with the [001] direction parallel to which the edge shared octahedra building its structure form infinite chains. FeNbO4 has the highest coefficients of thermal expansion in this group of compounds.

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Abstract  

The temperature dependence of unit cell parameters for KPb2Br5, RbPb2Cl5 and K0.5Rb0.5Pb2Br5 crystals was studied in the range of 100 to 298 K. Linear and volume thermal expansion coefficients were determined. Analysis revealed the thermal expansion effect on formation of nets of twin boundaries in crystals.

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Abstract  

A new method to measure heat flux and thermal expansion simultaneously with a temperature resolution of milli-Kelvin is presented to observe the multistage transitions. At least six thermal anomalies are observed between 402 and 403 K in BaTiO3 simultaneously in heat flux and thermal expansion in the cooling process. The correspondence of the anomalies observed in the two physical properties is excellent.

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Abstract  

The relationship between heat capacity (C p) and linear thermal expansion (α) derived from the Lennard–Jones potential is C p=Aα(U 0E), where U 0 is the heat of sublimation at T=0, E is the enthalpy and A is the coefficient. The values of A for different solidified inert gases coincide with one another within the limits of experimental error (±2%). The relationship is shown to be valid for various substances: solidified rare gases, diamond, halite and copper.

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Abstract  

Phase transition process of polyester from phenanthrene, poly(oxyheptamethyleneoxy-2,7-phenantrenedicarbonyl), a main chain type liquid crystalline polymer, was investigated by simultaneous DSC-XRD measurements using the synchrotron radiation facility (PF). Three exothermic DSC peaks were observed during cooling from the isotropic liquid state. These DSC peaks were assigned to the transition from the isotropic liquid to the smectic A, that from the smectic A to C, and that from the smectic C to the crystalline state, respectively, as determined by XRD profiles. The rate of transition from the smectic A to C was very slow compared with the liquid crystalline transition and the crystallization. From the DSC-XRD results, the thermal expansion along c-axis in the crystal and smectic phases are 4.110−4 and 1.410−3 nm K−1 , respectively.

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Abstract  

A5–4xZrxZr(PO4)3 (A=Na, K;0≤x≤1.25), Na1-xCd0.5xZr2(PO4)3 (0≤x≤1), Na5–xCd0.5xZr(PO4)3 (0≤x≤4) compositions which belong to the NZP structural family were synthesized using the sol-gel method. The lattice thermal expansion of members of these rows were determined up to 600C by high-temperature X-ray diffractometry. The axial thermal expansion coefficients change from -5.810-6to 7.510-6 C-1a) and from 2.610–6 to 2210–6 C-1c). These results, in addition to those for other NZP compounds allow us to explain their low thermal expansion. The mechanism can be attributed to strongly bonded three-dimensional network structure, the existence of structural holes capable to damp some of the thermal vibrations and anisotropyin the thermal expansion of the lattice.

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Negative thermal expansion materials

Thermal properties and implications for composite materials

Journal of Thermal Analysis and Calorimetry
Authors: Michael Jakubinek, Catherine Whitman, and Mary White

Abstract  

Finite element analysis is used to explore composites of negative thermal expansion materials with positive thermal expansion materials (ZrW2O8 in Cu and ZrO2 in ZrW2O8) and evaluate how thermal and mechanical properties, rates of cooling/heating, and geometry and packing fraction influence the overall expansion and thermal stress. During rapid temperature changes, the transient short-time thermal expansion can be considerably larger than the steady-state value. Furthermore, thermal stress in the composite can be large, especially at the interface between the materials, and can exceed the material strength.

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Journal of Thermal Analysis and Calorimetry
Authors: Aleksandra Yu. Tarasova, Yu. V. Seryotkin, V. M. Pashkov, and Ludmila I. Isaenko

communication lines. Unfortunately, there is a problem of twin formation in some parts of the boule [ 3 ]. The coefficient of linear thermal expansion (CLTE) is one of the most important parameters, which affects the twin formation when cooling crystal. It is

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pressure ( p ) and moles ( n ) ( Cp ) is defined as shown in Eq. 1 where enthalpy = H and temperature = T . 1 The coefficient of thermal expansion ( α ) is a volumetric ( V ) change defined by Eq. 2 and is analogous to the heat capacity in

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