Dissertation/Thesis Abstract

Single Crystal Growth of High Melting Oxide Materials by Means of Induction Skull Melting
by Paun, Matthias Stephan, Ph.D., Technische Universitaet Berlin (Germany), 2015, 148; 10704122
Abstract (Summary)

Various high melting oxide single crystals were grown by implementation of the induction skull melting technique. This technique can be described of a combination of high frequency induction heating and a water cooled crucible. Various single crystals were successfully grown; alkaline earth zirconates, transition metal doped titania and rare earth element (REE) doped yttrium stabilized zirconium dioxide (YSZ). The grown alkaline earth zirconate single crystals are CaZrO3, SrZrO3 and BaZrO3 and belong all to the perovskite structure type. CaZrO3 and SrZrO3 exhibit both an orthorhombic distortion and they crystalize in space group Pnma while BaZrO3 is belonging to the cubic aristotype Pm3m. The two orthorhombic zirconate crystals are featuring twins. The twinning emerged through the transformation from cubic to orthorhombic and the loss of symmetry. SrZrO3 single crystals were grown twice; under air and nitrogen atmosphere. The UV-Vis. reflection spectroscopy measurements revealed that the absorbance of both SrZrO3 samples differ from each other, especially at lower wavenumbers. SrZrO3 also shows luminescence effects when excited at approximately 260 nm. The emission spectra also differ between the two SrZrO3 samples. It is suggested that a small amount of nitrogen incorporated in the lattice is responsible for this effect. CaZrO3 was used as substrate for the growth of multiferroic materials carried out at the Institute of Crystal Growth in Berlin (IKZ). K0.8Na0.2NbO3 layers were successfully grown on CaZrO3. However, the twinning present above described resulted in an overall poor quality of the multiferroic material. TiO2 single crystals with five different transition metal dopants (Ni, Fe, Co, Mn, Nb) were successfully grown. The doping should ensure a decrease in optical band-gap of the host material (~3 eV). All titania crystals have a tetragonal rutile structure and belong to the space group P42/mnm. Optical reflectance measurements, in combination with the Kubelka-Munk model, revealed a successful decrease of the optical band-gap compared to the undoped host material. The ICP-OES measurements show an overall good correlation with the theoretical composition. Several yttrium stabilized zirconium dioxide (YSZ) single crystals with various REE (co-)dopants (Eu, Er, Yb, Tb, Tm) were successfully grown for the first time as part of this work. All phases are cubic and belong to the space group Fm3m (CaF2 structure type). The crystals feature a fluorescence effect by UV light due to the REE doping as well as a thermochromic effect in the case of Tb:YSZ. The high temperature UV-Vis. spectroscopy showed that Tb doped YSZ was also the only sample which has a higher optical absorbance at higher temperatures. The absorbance remained at a higher magnitude even after the cooling.

Indexing (document details)
Advisor: Lerch, Martin
School: Technische Universitaet Berlin (Germany)
School Location: Germany
Source: DAI-C 81/1(E), Dissertation Abstracts International
Subjects: High Temperature Physics, Condensed matter physics
Keywords: High-melting oxides, Single crystal growth
Publication Number: 10704122
ISBN: 9781392355961
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