Thermal Expansion Studies Research Articles

Preparation, characterization, conductivity and thermal expansion studies of Ca0.5SbMP3O12 (M = Al, Fe, Cr)

Nasicon type compounds of general formula Ca0.5SbMP3O12 (M = Al, Fe, Cr) are prepared by solid-state method. All the compounds crystallize in hexagonal lattice with \( R \,\bar 3\,c \) space group. The IR spectra show characteristic PO4 vibrations. Conductivity studies indicate the presence of charged defects. The Cole-Cole plots of impedance are semicircles between 150 and 350 °C. The thermal expansion of these samples is studied in the temperature range 25–500 °C.

Thermo acoustic parameters in the nematic and isotropic phases of 5CB and tetraethyl methane in 5CB

The addition of non-rod like solute impurity to a liquid crystalline solvent leads to some exciting results such as depression of nematic–isotropic transition temperature and the formation of two-phase region. In view of this, specific volume and thermal expansion studies in the nematic and isotropic phases of p- n-pentyl- p 1-cyanobiphenyl (5CB) and dilute solution of the quasispherical solute tetraethyl methane were considered. From these results thermo acoustic parameters such as isochoric temperature coefficient of internal pressure ( X), isochoric volume expansivity ( X 1), the reduced compressibility ( β ∼), the reduced volume ( V ∼), isothermal microscopic Gruneisen parameter ( Γ), Huggins parameter ( F), fractional free volume ( f) and Sharma parameter ( S o) are estimated both in nematic and isotropic regions. Using the data given by Oweimreen et al. [G.A. Oweimren, A.K. Shihab, K. Halhouli, S.F. Sikander, Mol. Cryst. Liq.Cryst. 138 (1986) 327] variations of these thermo acoustic parameters with temperature and two phase region are critically examined.

Thermal expansion study of spinel-sialon

The thermal expansion behaviour of a high pressure-derived spinel sialon ( γ -Si 3− x Al x O x N 4− x ) with a single composition x = 1.1 (and its low-pressure pendant with β -Si 3 N 4 structure) was studied between room temperature and 1220 ° C, using X-ray diffraction at a synchrotron radiation source and a halogen mirror furnace. No evidence for a phase transformation or decomposition of the spinel-sialon was found, thus demonstrating a good metastability of this novel hard material.

Uniaxial pressure dependencies of the phase boundary of TlCuCl 3

We present a thermal expansion and magnetostriction study of TlCuCl 3, which shows a magnetic-field-induced transition from a spin gap phase to a Néel-ordered phase. Using Ehrenfest relations we derive huge and strongly anisotropic uniaxial pressure dependencies of the respective phase boundary, e.g., the transition field changes by about ± 185 % / GPa depending on the direction of uniaxial pressure.

Thermal expansion study on high-pressure phases of SmS

We have measured the thermal expansion coefficient α L ( T ) of SmS under pressure up to 21.6 kbar. In the golden phase, an excitation gap Δ inferred from α L ( T ) decreases with increasing pressure. When the system enters the metallic phase from the golden phase, Δ collapses suddenly to zero, and simultaneously, a huge sharp anomaly appears in the α L ( T ) curve, reflecting the magnetic phase transition.

Thermal expansion studies on aluminium-matrix composites with different reinforcement architecture of SiC particles

The thermal expansion behaviour of different SiC particulate reinforced aluminium-matrix composites is investigated up to 500 °C using a thermal mechanical analysis equipment. The aim is to explain abnormalities in the thermal expansion behaviour of 70 vol% SiC particulate reinforced aluminium-matrix composites (Al/SiC) used as base plate material for high power electronic modules. Composites with different SiC contents (10, 20, 55, 70 vol%), various matrix-alloy compositions (Al99.5, A356, A359), and different fabrication routes are investigated. The instantaneous coefficient of linear thermal expansion (CTE) as a function of temperature is compared with predictions from thermo-elastic models according to Schapery and Turner using the expansion data determined for the ingredients. The expansion behaviour is correlated to the microstructure, the deformation of the matrix, and the internal stress conditions. The temperature dependence of the solubility of Si in Al influences the CTE of Al–Si matrix alloys significantly. Composites with isolated ceramic particles (10–55 vol%) show similar thermal behaviour as the matrix alloy just reduced by the volume fraction of SiC-particles. The CTE of highly reinforced Al/SiC(>55 vol% SiC), where the reinforcement is interconnected, drops above 250 °C. Such anomalies in the CTE are explained qualitatively by visco-plastic matrix deformations and changing void volume fractions. Although the matrix deforms non-elastic, the effects are reversible during reproduced thermal cycling.

Optical Birefringence and Domain Structure of the as-grown Rb2xTl2(1-x)Cd2(SO4)3 Solid Solutions at Phase Transitions

It is shown that the as-grown solid solutions Tl2xRb2(1-x)Cd2(SO4)3 possess a residual optical birefringence in the cubic phase at room temperature. The existence of both the residual birefringence and the residual domain structure in the compound with x=0.8 at the room temperature, along with the domain walls orientation and the orientation of extinction positions of the neighbouring domains, indicate that the above domain structure corresponds to forbidden ferroelastic domains of the phase P212121. On the basis of measurements for the temperature variation of the birefringence and observations of the domain structure transformations, one can conclude that the phases with the symmetries P213 and P21 coexist above Tc1 in the compounds with x = 0.7 - 1.0. The phase transition temperatures Tc1, Tc2, and Tc3 obtained from the temperature birefringence variations agree well with those obtained previously, using the studies of thermal expansion and ultrasonic wave velocities.

Pyroelectric and Dilatometric Studies on the Low Temperature Ferroelectric Phase Transition of (CH3NH3)5Bi2Br11

The results of the linear thermal expansion studies on (CH3NH3)5Bi2Br11 single crystals in the temperature range 60–340 K are presented. The thermal anomaly in the vicinity of 77 K is assigned to the phase transition classified as close to first order type. The pyroelectric measurements of (CH3NH3)5Bi2Br11 were carried out in the range of 45–320 K along the aand c-axis. The step-like change in the spontaneous polarization along the a-axis at 77 K indicates a discontinuous character of ferroelectric transition.

Low temperature structural and thermal expansion studies on α-cristobalite type Al 0.5Ga 0.5PO 4 by powder neutron diffraction

The orthorhombic (α) low-cristobalite type Al 0.5Ga 0.5PO 4, prepared by co-precipitation followed by high-temperature annealing of the amorphous precipitate has been investigated by powder X-ray diffraction (XRD) at room temperature and variable temperature neutron diffraction technique down to 20 K. In the temperature range of 20–300 K, the crystal structure of this compound has been analyzed by Rietveld refinements of powder neutron diffraction data. This composition crystallizes in the orthorhombic lattice with unit cell parameters: a = 7.030(1), b = 7.015(1), c = 6.923(1) Å and V = 341.4(1) Å 3 (space group C222 1) (at ambient temperature). The unit cell parameters show a gradual decrease with decreasing temperature and the Al 3+ and Ga 3+ ions are statistically distributed over a single crystallographic site forming an ideal solid solution of AlPO 4 and GaPO 4 down to 20 K. The structural details and low-temperature thermal expansion behavior of this compound are reported in this communication. The results are also compared with our earlier thermal expansion studies of cristobalite type phosphates above ambient temperature.

Phase relations and lattice thermal expansion studies in the Ce 0.50RE 0.50O 1.75 (RE = rare-earths)

The synthesis, characterization and lattice thermal expansion of a series of compounds with the general composition Ce 0.50RE 0.50O 1.75 (RE = trivalent rare-earth ion) are being reported. XRD pattern of each product was refined to know the lattice parameters in each case under the conditions of slow-cooling from 1400 °C. It was observed that the compositions with a 50 mol% of REO 1.5 substitution (RE = La to Ho) were all cubic solid solutions (either F-type or C-type). A steady decrease in the cubic lattice parameter value was observed on going from La to Ho, in the Ce 0.50RE 0.50O 1.75 series. The compositions with a 50 mol% of REO 1.5 substitution (RE 3+ = Er 3+, Yb 3+, Lu 3+ and Sc 3+) were found to be biphasic. The lattice thermal expansion behavior, as investigated by a high temperature-XRD, for each composition in the temperature range 293–1473 K is also being reported.

Lattice thermal expansion studies of Th 1− xNd xO 2− x/2 solid solutions

The synthesis, characterization and lattice thermal expansion studies of the ThO 2–Nd 2O 3 phase with general compositions Th 1− x Nd x O 2− x/2 are reported. Based on XRD data the composition corresponding to solid solubility limit of NdO 1.5 in ThO 2 lattice under conditions of slow cooling from 1673 K was previously reported as Th 0.50Nd 0.50O 1.75. The lattice thermal expansion (293–1473 K) behavior of the solid solutions has been investigated by high temperature XRD and found to show a gradual increase with increasing content of NdO 1.5 in Th 1− x Nd x O 2− x/2 series.

Synchrotron X-ray radiation diffraction studies of thermal expansion, free volume change and glass transition phenomenon in Cu-based glassy and nanocomposite alloys on heating

Thermal expansion and volume changes due to structural relaxation during heat treatment in glassy alloys were studied in situ using Synchrotron X-ray radiation diffractometry. A glass transition phenomenon was also detected. Synchrotron X-ray radiation diffractometry was successfully used for studying dilatation, glass transition and volume change phenomena detecting excess free volume and in glassy alloys. Good correspondence of the thermal expansion coefficients was obtained independently by thermo-mechanical length change measurements and Synchrotron X-ray radiation diffractometry as well as the glass transition temperature obtained by DSC and Synchrotron X-ray radiation diffractometry. The reduced average free volume change is smaller in the alloy consisting of the glassy matrix containing the nanocrystalline phase compared to the fully glassy alloy.

Preparation and Bulk Thermal Expansion Studies in M1‐xCexSiO4 (M: Th, Zr) System, and Stabilization of Tetragonal ThSiO4.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Phase relations and thermal expansion studies in the CeO 2–NdO 1.5 system

The synthesis, characterization, bulk and lattice thermal expansion of a series of compounds with general composition Ce 1− x Nd x O 2− x/2 , (0.0 ≤ x ≤ 1.0) are being reported in this manuscript. XRD pattern of each product was refined to know the solid solubility limit and the homogeneity range. The solid solubility limit of NdO 1.5 in CeO 2 lattice, under the conditions of slow cooling from 1400 °C, is represented as Ce 0.50Nd 0.50O 1.75 (i.e., 50 mol.% of NdO 1.5). There was no solubility of CeO 2 into the hexagonal lattice of NdO 1.5. The C-type Nd 3+ rich phases were also observed in this series. The bulk thermal expansion measurements from ambient to 1123 K, as investigated by a dilatometer, revealed that the α l (293–1123 K) values, within the cubic homogeneity range, decrease on increasing the Nd 3+ content. A similar trend was observed for average lattice thermal expansion coefficient, α a (293–1473 K), as investigated by a high temperature XRD. These studies on Ce 1− x Nd x O 2− x/2 , (0.0 ≤ x ≤ 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu 1− x Nd x O 2− x/2 , (0.0 ≤ x ≤ 1.0) as CeO 2 is widely used as a surrogate material for PuO 2.

Phase relations and linear thermal expansion of cubic solid solutions in the Th 1− xM xO 2− x/2 (M = Eu, Gd, Dy) systems

Cell parameters and linear thermal expansion studies of the Th–M oxide systems with general compositions Th 1− x M x O 2− x/2 (M = Eu 3+, Gd 3+ and Dy 3+, 0.0 ⩽ x ⩽ 1.0) are reported. The XRD patterns of each product were refined to specify the solid solubility limits of MO 1.5 in the ThO 2 lattice. The upper solid solubility limits of EuO 1.5, GdO 1.5 and DyO 1.5 in the ThO 2 lattice under conditions of slow cooling from 1673 K are represented as Th 0.50Eu 0.50O 1.75, Th 0.60Gd 0.40O 1.80 and Th 0.85Dy 0.15O 1.925, respectively. The linear thermal expansion (293–1123 K) of MO 1.5 and their single-phase solid solutions with thoria were investigated by dilatometery. The average linear thermal expansion coefficients ( α ¯ ) of the compounds decrease on going from EuO 1.5 to DyO 1.5. The values of α ¯ for EuO 1.5, GdO 1.5 and DyO 1.5 containing solid solutions showed a downward trend as a function of the dopant concentration. The linear thermal expansion (293–1473 K) of the solid solutions investigated by high-temperature XRD also showed a similar trend.

Lattice thermal expansion studies on single-phase compositions in CeO 2–ThO 2–ZrO 2 system

Earlier we reported the phase relations in the CeO 2–ThO 2–ZrO 2 system under slow cooled conditions from 1400 °C; ceria was used as a surrogate material for plutonia. A number of single-phase compositions with fluorite-type structure were identified in this pseudo-ternary system. For example, about 5 and 20 mol% of zirconia could be dissolved in the lattice of thoria and ceria, respectively. 10 mol% zirconia was incorporated in the lattice of Th 0.5Ce 0.5O 2. The lattice thermal expansion behaviour of a number of single-phase compositions in the temperature range from 293 to 1473 K, as investigated by high temperature XRD, are reported. For example, the average lattice thermal expansion coefficient of pure thoria was found to be 9.58 × 10 −6, which increased to 11.91 × 10 −6 K −1 in the composition Th 0.05Ce 0.90Zr 0.05O 2.

EXAFS studies of lattice dynamics and thermal expansion

1 Introduction The acronym EXAFS (Extended X-ray-Absorption Fine-Structure) refers to the oscillations observed on the high-energy side of x-ray absorption edges in molecules and condensed systems [1]. EXAFS can be interpreted, within the framework of the time-dependent perturbation theory, as a final state effect due to the interaction of the photo-electron with the neighbouring atoms, the frequencies of oscillations being directly connected to inter-atomic distances. Selectivity of atomic species and insensitivity to long-range order make EXAFS a powerful probe of the local structure in disordered systems (glasses, random alloys, catalysts, proteins, etc.) Accurate temperature-dependent measurements can also give information on lattice dynamics of crystals, owing to EXAFS sensitivity to the correlation of atomic vibrations. The difference between the Debye-Waller factors of EXAFS and diffraction, quite early recognized [2], is due to the correlation parallel to the bond direction. The difference between the interatomic distances measured by EXAFS and diffraction, more recently evidenced [3], is due to the perpendicular relative vibrations. The sensitivity of EXAFS to the real expansion of selected atomic bonds and to the perpendicular correlation can be exploited to study the local behaviour of some crystals affected by macroscopic Negative Thermal Expansion (NTE). In this paper, after a short account of basic concepts (Section 2), the results obtained for copper and germanium will be critically compared (Section 3). Section 4 will be dedicated to NTE and to some preliminary results on cuprite crystals. Conclusions will be drawn in Section 5.

Synthesis, phase transition and thermal expansion studies on M 2MgWO 6 (M = Ba 2+ and Sr 2+) double perovskites

The high-temperature behavior of Ba 2MgWO 6 and Sr 2MgWO 6 double perovskite compounds is studied by high-temperature XRD (HT-XRD) and dilatometer. At ambient temperature, Ba 2MgWO 6 crystallizes in cubic symmetry with space group Fm-3 m ( a = 8.1345(2) Å and V = 538.26(2) Å 3, Z = 4). The later compound crystallizes in tetragonal symmetry with space group I4/ m ( a = 5.5876(1) and c = 7.9490(3) Å; V = 248.18(1) Å 3, Z = 2). HT-XRD studies on these compounds were carried out in the temperature range of 25–1200 °C at each 100 °C interval in the static air atmosphere. Ba 2MgWO 6 is found to expand linearly in the studied temperature range. At and above 300 °C, a cubic elpasolite-type phase is observed for Sr 2MgWO 6. Within the tetragonal lattice, this compound shows anisotropic expansion. In the temperature range of 25–1200 °C, the typical volume thermal expansion coefficients of Ba 2MgWO 6 and Sr 2MgWO 6 are 35.6 × 10 −6 and 39.6 × 10 −6 /°C, respectively. The details of the phase transition and thermal expansion are explained in this manuscript.

Preparation and bulk thermal expansion studies in M 1− xCe xSiO 4 (M = Th, Zr) system, and stabilization of tetragonal ThSiO 4

Two series of compositions with the general formula M 1− x Ce x SiO 4 (M = Th, Zr; x = 0.0–0.5; 1.0) were prepared by a standard solid state route and characterized by powder XRD. About 10 mol% of ceria could be dissolved in the lattice of ThSiO 4. A striking observation was the stabilization of tetragonal modification of ThSiO 4, which is metastable, by ceria substitution. There was no solubility of ceria in zircon (ZrSiO 4) lattice. The average linear thermal expansion coefficient (293–1123 K) of ZrSiO 4, ThSiO 4 and Th 0.9Ce 0.1SiO 4 are 4.65 × 10 −6, 4.97 × 10 −6 and 5.14 × 10 −6 K −1, respectively.

Phase Relations and Thermal Expansion Studies in the Ceria–Yttria System

The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Ce1–xYxO2–x/2 (0.0 ≤x≤ 1.0) are reported. The XRD pattern of each product was refined to learn the solid solubility limit and the homogeneity range. The solid solubility limit of YO1.5 in CeO2 lattice, under the conditions of slow cooling from 1400°C, is represented as Ce0.55Y0.45O1.775 (i.e., 45 mol% of YO1.5). The subsequent compositions were biphase. There was no solubility of CeO2 into the lattice of YO1.5. The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the αl (293–1123 K) values, within the homogeneity range, decreased on increased Y3+ content. A similar trend was observed for average lattice thermal expansion coefficient, αa (293–1473 K), as investigated using high‐temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce1–xYxO2–x/2 (0.0 ≤x≤ 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu1–xYxO2–x/2 (0.0 ≤x≤ 1.0), because CeO2 is widely used as a surrogate material for PuO2.