No abstract

Mossbauer study of ordering in FeSi alloys.

Temperaturedependent first-order Raman scattering studies in the range 30-290 K were carried out in LicsSO, in order to investigate its phonon spectra in relation to the phase transitions in the crystal Complete spectra were obtained for the z(xx)p and z(xz)y geometries. A careful analysis of the spectra shows that both the low-and higb-energy Raman modes exhibit variations either in frequency or intensity or both with temperature of the crystal, indicating that the D,, normal phase undergoes a transition at the TI (202 K) and one to the commensurate phase at ca 160 K (T,). Below the T,, in the C,, phase, the lattice mode at 44 cm-' was observed to be a soft phonon with its frequency decreasing to 32 cm-' at 30 K, indicnting the possibility of a new structural phase transition of unlocking type in the crystal at a temperature T-below 20 K. Another observation is the oscillating behaviour of Rayleigh scattering near the phase transition at the TI.

Sintering studies were conducted using kaolin, metakaolin, zeolite 4A, and various synthetic mixtures of Al 2 O 3 and SiO 2 in the presence of Li 2 CO 3 and LiCl as fluxing agents. Various compositions of the above were prepared, and conventional sintering studies were conducted at temperatures of 900°-1450°C with soaking periods of 1-3 h. Kaolin, metakaolin, and amorphized kaolin in the presence of Li 2 CO 3 showed nucleation centers of ␤-spodumene as pink specks, whereas synthetic mixtures of Al 2 O 3 and SiO 2 failed to behave in the same manner. To determine whether the pink specks formed were color centers or F centers, the samples were subjected to UV, IR, and X-ray irradiation; however, the samples showed no tenebrescence properties. External addition of iron as an impurity in a nonlayered system also resulted in pink speck formation. This observation indicated that impurities present in the natural kaolin were the cause of this phenomenon. Moreover, the LiCl-based samples did not result in pink specks, even though the kaolinitic samples contained iron as an impurity. Therefore, although ␤-spodumene was formed in aluminosilicates in the presence of Li 2 CO 3 and LiCl, the pink variety of ␤-spodumene (kunzite) formation occurred only in the presence of lithium-rich aluminosilicates and in the presence of iron as an impurity. The phase identification and microstructure were explained based on XRD, DTA, and SEM studies.

Polarized first-order Raman spectra of B e 0 crystal were recorded at various temperatures to study the variations in frequencies and intensities associated with some of the phonons. At 35 K five modes were assigned to be fundamentals at 338.1 682.6, 686.6, 726.7 and 1085.8 cm-'. The different scattering geometries were utilized to study the directional dependence of the dipolar phonons. Two peaks at 703.6 and 1093.7 cm-l were the quasi-TO and LO modes, respectively. Both the frequency and the intensity of the phonons increase with decreasing temperature. The mode at 682.6 cm-' was examined in more detail at several temperatures.