The heat capacity and thermal expansion of ${\mathrm{SrZrO}}_3$ and ${\mathrm{SrTiO}}_3$ have been determined by drop calorimetry and energy-dispersive x-ray diffraction from 300 up to 1800 K or more. For both compounds, thermal history has a slight influence on relative enthalpies in the range 900–1400 K but a satisfactory precision was obtained through systematic quenches from 1820 K before the calorimetric measurements. Strontium titanate is cubic at room temperature. Up to 1800 K, its heat capacity increases smoothly and its thermal-expansion coefficient remains almost independent of temperature with a value of 3.23(2) ${10}^{\mathrm{-}5}$ ${\mathrm{K}}^{\mathrm{-}1}$. At room temperature, strontium zirconate is orthorhombic (space group Pbnm). The phase transitions from orthorhombic Pbnm to orthorhombic Cmcm at 995 K and then to tetragonal I4/mcm at 1105 K are revealed by symmetric, λ-type variations of the heat capacity. A more diffuse thermal effect characterizes the I4/mcm to cubic Pm3m transition at 1440 K, above which the cubic phase shows an apparently low heat capacity at the highest temperatures. With the resolution of the x-ray technique, only the transition from orthorhombic Pbnm to orthorhombic Cmcm at 970 K was detected with a small volume change of 0.14%. Thermal expansion below 970 K is constant at 2.98(2) ${10}^{\mathrm{-}5}$ ${\mathrm{K}}^{\mathrm{-}1}$. At higher temperatures, the apparent thermal expansion decreases smoothly from 2.78(2) to 2.43(2) ${10}^{\mathrm{-}5}$ ${\mathrm{K}}^{\mathrm{-}1}$ between 1000 and 1800 K. With recent data on ${\mathrm{CaTiO}}_3$, the effects of (Ca,Sr) and (Ti,Zr) substitutions on thermal expansion and on the energetics of the phase transitions are discussed. © 1996 The American Physical Society.

When monochromatic radiation ν_o, is incident on a system (gas, solid, liquid, glass, whether colored or transparent) most of the radiation is transmitted through the system without change, but some scattering of this radiation can also occur (approximately 1 in 10⁷ photons). The scattered radiation corresponds to ν′ = ν_o ± ν_m. In molecular systems, the energy of the scattered light (in wavenumbers, ν_m) is found to lie principally in the range associated with transitions between vibrational, rotational and electronic energy levels. Furthermore, the scattered radiation is generally polarized differently from that...

The influence of the temperature and quenching rate on the structure of a borosilicate glass was studied by high-resolution solid-state 11B, 23Na, 29Si nuclear magnetic resonance (NMR) and high-temperature Raman spectroscopy. Data were obtained for glass in the solid state after annealing and quenching at cooling rates covering four orders of magnitude as well as in the liquid state from Raman experiments and from calorimetry and rheological data. Nuclear magnetic resonance measurements were used to calibrate the Raman spectra in order to quantify the change in boron coordination with temperature. This result can then be used to determine the fictive temperature of the glass directly from the boron coordination. The fictive temperature, heat capacity, and configurational entropy are extracted from calorimetry and viscosity measurements. Changes in the boron coordination account for only 25% of the configurational heat capacity of the liquid. The structural parameters capable of accounting for the remaining quantity are discussed on the basis of structural data, both local (inhomogeneity of the sodium distribution) and medium-range (from NMR parameter distribution). It has thus been shown that, although the B-O-B angular distributions of the boroxol rings (and probably the Si-O-Si distributions) are not affected by temperature, a structural disorder is identified through the angular distributions of the bonds linking borate and silicate groups.