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
Axial and low-symmetry centers of trivalent impurities in lithium niobate: Chromium in congruent and stoichiometric crystals
A systematic analysis and classification of clusters, consisting of impurity ~ex rinsic! and intrinsic defects in lithium niobate crystals, were made in order to understand the main features of the observed EPR spectra. It is shown that possible configurations for lithium substitution with charge compensators such as a lithium vacancy (XLi-YLi), niobium vacancy ( XLi-YNb), and oxygen interstitial ions ( XLi-Yi) belong toC3 or C1 point group symmetries; this is also valid for the complexes with niobium substitution and the Nb Li antisite as the compensator ( XNb-YLi). Clusters of an oxygen vacancy and an impurity on a niobium site ~XNb-YO configurations ! haveC1 symmetry only, but never C3 symmetry. A detailed study of EPR spectra for a wide set of crystals with different chromium concentrations and @Li #/@Nb# ratios was carried out. Besides the main axial Cr 31
Composite monolayer fabrication by an arc-spray process
A single layer (monotape) technique for fabricating complex high-temperature tungsten-fiber-reinforced superalloy composites is proposed. The fabrication of sheets of arc-sprayed monotape 38 cm wide and 122 cm long has been demonstrated. Composites fabricated using the method are shown to have equal tensile strength and a cleaner matrix than composites fabricated from powder metal cloth monotapes, and the present technique is less expensive than the powder metal fabrication techniques.