Average Linear Thermal Expansion Coefficient Research Articles

Growth and thermal properties of Co 2+:LaMgAl 11O 19 crystal

The 0.5 and 1 at% Co 2+-doped lanthanum magnesium hexaluminates (LaMgAl 11O 19, LMA) polycrystalline material was synthesized with high-purity (99.99%) La 2O 3, MgO, Al 2O 3 and analytical purity Co(CH 3COO) 2·4H 2O by the solid-state reaction technique. The blue Co 2+:LMA single crystal up to Φ 40×50 mm was successfully grown by the Czochralski method. X-ray powder diffraction (XRPD) results show that the as-grown Co:LMA crystal belongs to the hexagonal system and P6 3/mmc space group. X-ray fluorescence (XRF) analysis indicates that the effective segregation coefficient of Co 2+ ions in the Co:LMA crystal is k eff ( Co ) = 0.7487 . The high crystalline quality of the as-grown Co:LMA crystals was confirmed by High-resolution X-ray diffraction (HRXRD), which showed the full-width half-maximum (FWHM) of the rocking curves to be less than 20 arcsec on the (0 0 8) and (2 0 0) diffraction planes of the 0.5 at% Co:LMA crystal. The average linear thermal expansion coefficients are α 1 = 9.9720 × 1 0 - 6 / K , α 2 = 11.4451 × 1 0 - 6 / K and α 3 = 16.4328 × 1 0 - 6 / K for the 0.5 at% Co:LMA crystal and α 1 = 9.8753 × 1 0 - 6 / K , α 2 = 10.7768 × 1 0 - 6 / K and α 3 = 15.8901 × 1 0 - 6 / K for the 1 at% Co:LMA crystal in the temperature range from 300.15 to 1133.15 K along the three respective crystallophysical axes. The specific heat of the as-grown Co:LMA crystal increases from 565.36 to 825.12 J K −1 mol −1 when the temperature increases from 323.15 to 1163.15 K. The density of the as-grown Co:LMA crystals is measured by the buoyancy method at 22 °C and the results were 4.236 and 4.243 g cm −3 for 0.5 at% and 1 at% Co:LMA crystal, respectively. The thermal diffusion coefficient of the 0.5 at% Co:LMA crystal was measured in the temperature range of 298.15 to 563.15 K. The calculated thermal conductivity is 4.758 (3.238) W m −1 K −1 along the X 2 ( X 3) crystallophysical direction at 328.15 K. These thermal properties show Co:LMA crystal may be used in high-power laser system.

Thermophysical Properties of Perovskite‐Type Strontium Cerate and Zirconate

Polycrystalline samples of strontium series perovskite‐type oxides, SrCeO3 and SrZrO3, were prepared and the thermophysical properties were measured. The chemical compositions of the samples do not deviate from the stoichiometric composition. The oxygen‐to‐metal (O/M) ratios of SrCeO3 and SrZrO3 are 3.00±0.03 and 2.98±0.01, respectively. The average linear thermal expansion coefficients are 1.11 × 10−5 K−1 for SrCeO3 and 9.69 × 10−6 K−1 for SrZrO3 in the temperature range between 300 and 1000 K. The melting temperatures Tm of SrCeO3 and SrZrO3 are 2266 and 2883 K, respectively. The longitudinal and shear sound velocities were measured by an ultrasonic pulse–echo method at room temperature in air, which enables to evaluate the elastic moduli and Debye temperature. The heat capacity was measured by using a differential scanning calorimeter in high‐purity argon atmosphere. The thermal diffusivity was measured by a laser flash method in vacuum. The thermal conductivities of SrCeO3 and SrZrO3 at room temperature are 2.95 and 4.06 W·m−1·K−1, respectively.

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 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.

Hygroscopicity and bulk thermal expansion in Y 2W 3O 12

Negative thermal expansion material, Y 2W 3O 12 has been synthesized by the solid-state method and bulk thermal expansion of the material has been investigated from 300 to 1100 K. The material reversibly forms a trihydrate composition whose X-ray diffraction pattern can be indexed to an orthorhombic unit cell with a = 10.098(1) Å, b = 13.315(3) Å, c = 9.691(4) Å. The cell volume of the hydrated pattern is 7% smaller than the unhydrated cell volume. According to the dilatometric studies, the material shows a 3–6% increase in the linear strain at about 400 K, which can be attributed to the removal of water. Sintering the material at 1473 K leads to large grain size of >100 μm, which results in a large hysteresis in the bulk thermal expansion behavior. Hot pressing at 1273 K under a uniaxial pressure of 25 MPa results in a fine-grained (2–5 μm) ceramic. Glazing the ceramic prevents moisture pick up and a linear thermal expansion over the entire temperature range 1100–300 K and an average linear thermal expansion co-efficient of −9.65 × 10 −6/K is observed. The effect of water on the thermal expansion behavior of this system is discussed.

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.

Thermophysical properties of SrHfO3 and SrRuO3

Polycrystalline samples of strontium series perovskite type oxides, SrHfO3 and SrRuO3 were prepared and the thermophysical properties were measured. The average linear thermal expansion coefficients are 1.13×10−5K−1 for SrHfO3 and 1.03×10−5K−1 for SrRuO3 in the temperature range between 423 and 1073K. The melting temperatures Tm of SrHfO3 and SrRuO3 are 3200 and 2575K, respectively. The longitudinal and shear sound velocities were measured by an ultrasonic pulse-echo method at room temperature in air, which enables to evaluate the elastic moduli and Debye temperature. The heat capacity was measured by using a differential scanning calorimeter, DSC in high-purity argon atmosphere. The thermal diffusivity was measured by a laser flash method in vacuum. The thermal conductivities of SrHfO3 and SrRuO3 at room temperature are 5.20 and 5.97Wm−1K−1, respectively.

LaCrO<sub>3</sub> の熱膨張性と導電性に及ぼす Ti 置換の影響

Linear thermal expansion and electrical conductivity of titanium substituted LaCrO3 have been studied as ceramic interconnect materials in high-temperature solid oxide fuel cells. The transition temperature from orthorhombic to rhombohedral symmetry has a tendency to increase with decreasing Ti content in the perovskites. At Ti content ≥0.2, the phase transition was not observed in the temperature range from room temperature to 1273 K. Average linear thermal expansion coefficient of the Ti substituted perovskites increased with increasing Ti content and approaches that of 8 mol%Y2O3 stabilized ZrO2 electrolyte. Electrical conductivity of the lanthanum chromites decreased with increasing Ti content.

Evaluation of Ni and Ti-doped Y 2O 3 stabilized ZrO 2 cermet as an anode in high-temperature solid oxide fuel cells

The compatibility of nickel and Ti-doped 8 mol% Y 2O 3 stabilized ZrO 2 (Ni–Ti–YSZ) cermets has been discussed for use as an anode in high-temperature solid oxide fuel cells (SOFC). The solubility limit of TiO 2 in the YSZ fluorite was estimated to be at least 10 mol%. With increasing Ti content in the Ti–YSZ samples, the average linear thermal expansion coefficient was found to decrease when measured in an H 2 atmosphere. In an H 2 atmosphere, the oxygen vacancy concentration was observed to increase with increasing Ti content and temperature, and its value in the 8 mol% Ti-doped YSZ (8Ti–YSZ) sample was 0.0056 at 1000 °C. Although electronic conduction appeared in the Ti–YSZ samples at temperatures greater than ∼600 °C in the H 2 atmosphere, their electrical conductivities had a tendency to decrease with increasing Ti content. The mechanical strength of the Ni–Ti–YSZ cermets at room temperature were found to increase with increasing Ti content. Anodic polarization of the 40 vol.% Ni–8Ti–YSZ cermet at 1000 °C was 60 mV at 300 mA cm −2 in the H 2 atmosphere after firing at 1400 °C for 10 h.

Thermal Expansion of Simulated Spent PWR Fuel and Simulated DUPIC Fuel

Thermal expansions of simulated spent PWR fuel and simulated DUPIC fuel were studied using a dilatometer in the temperature range from 298 to 1900 K. The densities of simulated spent PWR fuel and simulated DUPIC fuel used in the measurement were 10.28 g⋅cm−3 (95.4% of TD) and 10.26 g⋅cm−3 (95.1% of TD), respectively. The linear thermal expansions of the simulated fuels are higher than that of UO2, and the difference between these fuels and UO2 increases progressively with temperature. However, the difference between simulated spent PWR fuel and simulated DUPIC fuel is extremely small, less than the experimental error. For the temperature range from 298 to 1900 K, simulated spent PWR fuel and simulated DUPIC fuel have the same average linear thermal expansion coefficient of 1.39×10−5K−1. As the temperature increases to 1900 K, the relative densities of simulated spent PWR fuel and simulated DUPIC fuel decrease to 93.8% of initial densities at 298 K.

Oxygen permeability of perovskite-type Sr 0.7Ce 0.3MnO 3− δ

The average linear thermal expansion coefficient (TEC) of perovskite-type Sr 0.7Ce 0.3MnO 3− δ , calculated from dilatometric data at 300–1100 K in air, is (11.9±0.2)×10 −6 K −1, compatible with that of stabilized zirconia. The high electronic conductivity, 230–270 S/cm at 773–1273 K, and the moderate thermal expansion suggest possible application of Ce-doped strontium manganite as solid oxide fuel cell (SOFC) cathode material. The oxygen permeation fluxes through dense Sr 0.7Ce 0.3MnO 3− δ membranes at 1273–1173 K were found to linearly increase with the oxygen chemical potential gradient in the range of permeate-side oxygen partial pressures from 21 kPa down to 2×10 −9 Pa, indicating a relatively high stability of this phase. However, the oxygen permeability of Sr 0.7Ce 0.3MnO 3− δ , limited by both bulk ionic conductivity and surface exchange at the membrane/gas boundaries, is higher than that of La 0.7Sr 0.3MnO 3− δ , but still considerably lower if compared to La(Sr)Fe(Co)O 3− δ perovskites.

Compatibility of Gd xTi 2O 7 pyrochlores (1.72≤ x≤2.0) as electrolytes in high-temperature solid oxide fuel cells

The crystal structure, sintering characteristics, electrical conductivity and thermal expansion of Gd x Ti 2O 7− δ pyrochlores (1.72≤ x≤2.10) have been studied as potential electrolytes in high-temperature solid oxide fuel cells (SOFC). It was found that the A-site deficiency of Gd x Ti 2O 7− δ with cubic symmetry showed a wide region of 1.72< x<2.03. A-site vacancies promoted the sintering characteristics of these materials. Electrical conductivity of the pyrochlores with A-site vacancies was lower than that of Gd x Ti 2O 7 in air although the reverse was observed in reducing atmospheres, due to the appearance of electronic conduction. Average linear thermal expansion coefficients of Gd x Ti 2O 7− δ pyrochlores decreased with increasing A-site vacancies. The difference between the TEC in air and in a H 2 atmosphere had a tendency to increase with increasing A-site vacancies.

Temperature-dependence of protein hydrogen bond properties as studied by high-resolution NMR

The temperature-dependence of a large number of NMR parameters describing hydrogen bond properties in the protein ubiquitin was followed over a range from 5 to 65°C. The parameters comprise hydrogen bond (H-bond) scalar couplings, h3JNC′, chemical shifts, amide proton exchange rates, 15N relaxation parameters as well as covalent 1JNC′ and 1JNH couplings. A global weakening of the h3JNC′ coupling with increasing temperature is accompanied by a global upfield shift of the amide protons and a decrease of the sequential 1JNC′ couplings. If interpreted as a linear increase of the N⋯O distance, the change in h3JNC′ corresponds to an average linear thermal expansion coefficient for the NH→O hydrogen bonds of 1.7×10−4/K, which is in good agreement with overall volume expansion coefficients observed for proteins. A residue-specific analysis reveals that not all hydrogen bonds are affected to the same extent by the thermal expansion. The end of β-sheet β1/β5 at hydrogen bond E64→Q2 appears as the most thermolabile, whereas the adjacent hydrogen bond I3→L15 connecting β-strands β1 and β2 is even stabilized slightly at higher temperatures. Additional evidence for the stabilization of the β1/β2 β-hairpin at higher temperatures is found in reduced hydrogen exchange rates for strand end residue V17. This reduction corresponds to a stabilizing change in free energy of 9.7 kJ/mol for the β1/β2 hairpin. The result can be linked to the finding that the β1/β2 hairpin behaves as an autonomously folding unit in the A-state of ubiquitin under changed solvent conditions. For several amide groups the temperature-dependencies of the amide exchange rates and H-bond scalar couplings are uncorrelated. Therefore, amide exchange rates are not a sole function of the hydrogen bond “strength” as given by the electronic overlap of donors and acceptors, but are clearly dependent on other blocking mechanisms.

Crystal structure, thermal expansion and electrical conductivity of Nd 0.7Sr 0.3Fe 1− xCo xO 3 (0≤ x≤0.8)

The crystal structure, thermal expansion and electrical conductivity of the solid solution Nd 0.7Sr 0.3Fe 1− x Co x O 3 for 0≤ x≤0.8 were investigated. All compositions had the GdFeO 3-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction (XRPD). The pseudo-cubic lattice constant decreased continuously with x. The average linear thermal expansion coefficient (TEC) in the temperature range from 573 to 973 K was found to increase with x. The thermal expansion curves for all values of x displayed rapid increase in slope at high temperatures. The electrical conductivity increased with x for the entire temperature range of measurement. The calculated activation energy values indicate that electrical conduction takes place primarily by the small polaron hopping mechanism. The charge compensation for the divalent ion on the A-site is provided by the formation of Fe 4+ ions on the B-site (in preference to Co 4+ ions) and vacancies on the oxygen sublattice for low values of x. The large increase in the conductivity with x in the range from 0.6 to 0.8 is attributed to the substitution of Fe 4+ ions by Co 4+ ions. The Fe site has a lower small polaron site energy than Co and hence behaves like a carrier trap, thereby drastically reducing the conductivity. The non-linear behaviour in the dependence of log σT with reciprocal temperature can be attributed to the generation of additional charge carriers with increasing temperature by the charge disproportionation of Co 3+ ions.

Thermal expansion of UO 2 and simulated DUPIC fuel

The lattice parameters of simulated DUPIC fuel and UO 2 were measured from room temperature to 1273 K using neutron diffraction to investigate the thermal expansion and density variation with temperature. The lattice parameter of simulated DUPIC fuel is lower than that of UO 2, and the linear thermal expansion of simulated DUPIC fuel is higher than that of UO 2. For the temperature range from 298 to 1273 K, the average linear thermal expansion coefficients for UO 2 and simulated DUPIC fuel are 10.471×10 −6 and 10.751×10 −6 K −1, respectively.

Thermal Expansion Behavior of Titanium‐Doped La(Sr)CrO3 Solid Oxide Fuel Cell Interconnects

La0.8Sr0.2Cr0.9Ti0.1O3 perovskite has been designed as an interconnect material in high‐temperature solid oxide fuel cells (SOFCs) because of its thermal expansion compatibility in both oxidizing and reducing atmospheres. La0.8Sr0.2Cr0.9Ti0.1O3 shows a single phase with a hexagonal unit cell of a= 5.459(1) Å, c= 13.507(2) Å, Z= 6 and a space group of R‐3C. Average linear thermal expansion coefficients of this material in the temperature range from 50° to 1000°C were 10.4 × 10−6/°C in air, 10.5 × 10−6/°C under a He–H2 atmosphere (oxygen partial pressure of 4 × 10−15 atm at 1000°C), and 10.9 × 10−6/°C in a H2 atmosphere (oxygen partial pressure of 4 × 10−19 atm at 1000°C). La0.8Sr0.2Cr0.9Ti0.1O3 perovskite with a linear thermal expansion in both oxidizing and reducing environments is a promising candidate material for an SOFC interconnect. However, there still remains an air‐sintering problem to be solved in using this material as an SOFC interconnect.

Relationship between the thermal expansion coefficient, plasmon energy, and bond length of ternary chalcopyrite semiconductors

A simple relation between the average bond length and plasmon energy, that is, d=15.30(ℏ ω p) −2/3, has been proposed for A IIB IVC V 2 and A IB IIIC VI 2 chalcopyrite semiconductors. The average linear thermal expansion coefficient ( α L) of these semiconductors has been calculated using plasmon energy data. The linear expansion coefficients ( α a ) and ( α c ) of the lattice parameters a and c, respectively, have also been calculated. The calculated values of d, α L, α a and α c have been compared with the experimental values and the values reported by different workers. A fairly good agreement has been obtained between them.

Control of the Thermal Expansion of Strontium‐Doped Lanthanum Chromite Perovskites by B‐site Doping for High‐Temperature Solid Oxide Fuel Cell Separators

The thermal expansion of La0.9Sr0.1Cr1‐xMxO3(M = Mg, Al, Ti, Mn, Fe, Co, Ni; 0 ≤x≤ 0.1) perovskites has been studied in oxidizing and reducing atmospheres in the temperature range from 50° to 1000°C. Cobalt doping of La0.9Sr0.1CrO3was an effective way of increasing the average linear thermal expansion coefficient (TEC), whereas titanium doping showed a negative effect. No effect on the TECs was observed for the B‐site dopants in perovskites with the remaining dopants. Linear thermal expansion behavior was observed in the La0.9Sr0.1Cr1‐xMxO3 perovskites with doping of ≥1 mol% aluminum or 10 mol% cobalt. TECs of La0.9Sr0.1Cr0.96Co0.02Al0.02O3 were 10.5 × 10−6/°C in air, 10.7 × 10−6/°C under He–H2 atmosphere (oxygen partial pressure of 4 × 10−15 atm at 1000°C), and 11.8 × 10−6/°C in H2 atmosphere.

Solubility limits and bulk thermal expansion of ThO 2:M n+ (M=Y 3+, Sr 2+ and Ba 2+)

In order to simulate the bulk thermal expansion behaviour of ThO 2 containing different amounts of fission products, a series of mixed oxides of ThO 2 and oxides of some major fission products (Ba 2+, Sr 2+ and Y 3+) were prepared and characterized by powder XRD. The upper solubility limit of these dopants was determined by following the change in lattice parameters as a function of their content. The bulk thermal expansion of the each product was investigated from ambient temperature to 1123 K using a dilatometer. The substitution of alkaline-earth ions and Y 3+ was shown to have the opposite effects on thermal expansion behaviour of ThO 2; e.g., in the presence of 12.5 mol% of Y 3+, the average linear thermal expansion coefficient α (293–1123 K) of ThO 2 decreased from 9.04×10 −6 to 8.27×10 −6 K −1. On the other hand, in the presence of 10.0 mol% of Ba 2+, the α (293–1123 K) of ThO 2 increased to 9.65×10 −6 K −1.

Bulk thermal expansion studies of Th 1− xCe xO 2 in the complete solid solution range

ThO 2 and CeO 2 are shown to form an almost ideal solid solution throughout the homogeneity range. Bulk thermal expansion studies on Th 1− x Ce x O 2 (0.0⩽ x⩽1.0) were carried out by dilatometry from 293 to 1123 K in air. The average linear thermal expansion coefficients, α ̄ , of ThO 2 and CeO 2 were found to be 9.04×10 −6 and 11.58×10 −6 K −1 , respectively, between 293 and 1123 K. The substitution of Ce 4+ at Th 4+ sites in ThO 2 induced a systematic upward trend in the thermal expansion behavior throughout this series of solid solution on going from ThO 2 to CeO 2.