Thermal physical properties of the La0.825Sr0.175MnO3 single crystals

The heat capacity (C _P), the thermal diffusion (η), the thermal conductivity (κ), and the electrical resistance of the La_0.825Sr_0.175MnO₃ single crystal have been measured in the temperature range 80–350 K in magnetic fields to 40 kOe. Dependences C _P(T), κ(T), and η(T) have anomalies near T _C, which are suppressed in magnetic field. The minima in dependences κ(T) and η(T) near T _C are explained by the phonon scattering on fluctuations of the magnetic order parameter. Dependences κ(T) and η(T) have anomalies near T _S = 200 K related to the structural transition from the rhombohedral (R) to the orthorhombic (O*) phase.

     

Electron Traps with a Wide Range of Capture Cross Sections in Powdery ZnS-Based Luminophors

Using the method of thermally stimulated luminescence, the phenomenon of spatial modulation of the capture cross section (S_t) of electron traps with a level of E_c − 0.18 eV in powdery luminophors Zn_0.97Cd_0.03S 〈Cu, Cl〉 with green luminescence and ZnS〈Ag, Cl〉 with blue luminescence by a collective electric field of macroinhomogeneity has been investigated. The maximum value of the effect (width of the range of values of S_t) attains five orders of magnitude, with the size of the powder grains being of order 1 µm. A model is suggested, according to which traps with E_c − 0.18 eV with an extended range of values of S_t represent an isolated anionic vacancy in a region of the collective field of macroscopic inhomogeneity that is the negatively charged surface of the powder grains. The extension of the range of values of S_t is the result of modulation of the kinetic parameters of electron traps E_c − 0.18 eV depending on the spatial position occupied by the anionic vacancy relative to the surface of the powder grains.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 202–206, March–April, 2005.