Low Temperature Crystal Structure Behaviour of Complex Yttrium Aluminium Oxides YAlO_3 and Y_3Al_5O_{12}

Abstract

Crystal structures of two yttrium aluminium oxides, namely YAlO3 and Y3Al5O12, were investigated in the temperature range 3.4300 K by high-resolution neutron powder diraction. Neither traces of phase transformations nor discontinuous changes of physical properties were observed. Thermal expansion of yttrium aluminium oxides was evaluated in terms of 1st order Grüneisen approximation, where the Debye temperatures and the Grüneisen parameters have been estimated for both compositions. Anomalies in the thermal expansion of yttrium aluminium perovskite have been observed and modelled using the Einstein oscillator with negative Grüneisen parameter. Extended bond length analysis revealed signicant thermally-driven modications of the aluminium oxygen framework.

Neutron diffraction study of Li 4 Ti 5 O 12 at low temperatures

“…The enhanced thermal rigidity of bonds in tetrahedral coordinations with nearly zero expansion or even weak tendency to contraction was already reported in the literature [39]. Furthermore, a similar dependence of octahedral AlO 6 and tetrahedral AlO 4 bondlengths was also found for Y 3 Al 5 O 12 garnet recently [40]. According to the work of Busing and Levy [41] observed nearly constant thermal behaviour of internal bonds in tetrahedral coordination can be explained by the "riding" model where corrections for parallel and antiparallel thermal motion have to be taken into account.…”

Vibrational Spectroscopy of YAlO3

“…Initial atomic coordinates for optimization are taken from Senyshyn (2013). [ 10 ] Basis sets are chosen not too large: one, to increase the speed and likelihood of convergence, and two, as the focus of this research is geared more toward experiment, with theory offering a supporting role. A triple zeta valence basis set is used for the aluminum and oxygen atoms while an effective core potential is used for the yttrium atoms.…”

The Application of Cryogenic Laser Physics to the Development of High Average Power Ultra-Short Pulse Lasers

“…In a few cases, however, the thermal expansion can become negative at lower temperatures, as may be seen in the YALO a-axis data in Figure 20, and the ZnO a and b axes data in Figure 27. In [61] the Grüneisen parameters for YAG and YALO are discussed, and the negative thermal expansion coefficient modeled as an additive negative Grüneisen parameter. .…”