Selection of some Raman spectra showing the dependence of PLT Raman modes as a function of (a) the La-composition at T = 8 K and atmospheric pressure, (b) the temperature at atmospheric pressure (2.5% La sample), and (c) the hydrostatic pressure applied to the 2.5% La sample and at room temperature.
Raman frequencies of PLT (2.5% La) at room temperature for different values of applied pressure. The dotted lines represent linear fittings for the vibrational modes.
Effect of temperature and pressure in the full width at half maximum (FWHM) in the Raman modes from the samples PLT. Figure depicts variations of the FWHM of Raman bands with temperature (a), or with applied pressure (b).
Low-frequency region of the Raman spectra for the 2.5% La sample. Observe the mode softening evolution and the redshift of E1(TO) with increasing applied hydrostatic pressure.
Average thermal expansion coefficient (TEC) of , as obtained from data reported by Chen et al. 1 The La datum for the 2.5% sample was extrapolated.
Calculated values of , and the Grüneisen parameter , at room temperature, for all active Raman modes and lanthanum concentrations of 10%, 15%, and 20%. Bulk modulus for a 10% La concentration was calculated using the lattice parameters obtained by Mota 14 at T = 150 K, assuming that these parameters are the same at room temperature.
Coefficients at constant volume. Explicit contribution of anharmonicity.
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