High Resolution XRD Studies on Mg, Cr and Nd Doped LiNbO3 Crystals
Undoped and doped LiNbO3 single crystals were grown by Czochralski technique. Comparative studies on these undoped, Cr doped, Mg doped, Mg:Cr codoped and Mg:Nd codoped LiNbO3 single crystals were carried out. Phase identification was done using powder XRD technique. The effect of doping and co-doping on crystalline perfection of these crystals was monitored using high resolution x-ray diffraction (HRXRD) technique. The diffraction curves (DCs) were recorded in symmetrical Bragg geometry for (006) diffracting planes using MoK￻ 1 radiation. tant is co-doping with Mg or Zn at a level above 4.5 mol%, which inhibits photorefractive properties of the material. Another potential application of LiNbO3 is in Nd 3+ based compact diode-pumped self-frequency doubled lasers that emit green radiation, useful for applications in optical data storage, and excitation sources to replace ion gas lasers and pumping of parametric oscillators and amplifiers (10). The
Assessment of the tunable laser crystal LiNbO3:Cr3+
The electronic structures of Cr3+ ions on the Nb site and the Li site of LiNbO3 were calculated under the actual site symmetry C3 with the spin-polarized self-consistent-charge discrete variational Xalpha (SCC-DV-Xalpha ) method. Special emphasis is placed on a discussion of the potential of LiNbO3:Cr3+ as a tunable laser crystal.
The pressure dependences of TiS2 and TiSe2 band structures
The band structures of the layer compounds 1T-TiS2 and 1T-TiSe2 have been calculated within the local-density approximation using the self-consistent LAPW method. Both compounds are found to be semimetals with Gamma -L overlaps of 0.24 and 0.55 eV, respectively. The positioning and occupation of the bands near the Fermi level are not consistent with the carrier densities determined from Hall measurements; however, agreement is obtained when the overlap is decreased by about 0.25 eV. Calculations performed with contracted lattice constants reproduce qualitatively the same trends in Hall coefficients as observed experimentally. However, quantitative agreement cannot be obtained without an overlap decrease of about 0.25 eV-indicating that TiSe2 is a semimetal and TiS2 a semiconductor.