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Origin of the negative thermal expansion in perovskite-type PrGaO₃

Anatoliy Senyshyn ², Leonid Vasylechko ², Dmytro I. Savytskii ², Ulrich Bismayer ¹, Marek Berkowski ³

1. University of Hamburg, Mineralogisch-Pertographisches Institut, Hamburg, Germany
2. Lviv Polytechnic National University, 12 Bandera, Lviv 79013, Ukraine
3. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland

Abstract

Perovskite-type rare-earth gallates attracted much attention because of their interesting physical qualities. Most important properties of RGaO₃ compounds are used in substrate materials, either for high-temperature superconductors (HTSC), for doped manganese perovskite LnMnO₃ films with colossal magnetoresistance (CMR) and for GaN films. Recently it was proposed to use rare-earth gallates as superionic conductors. Among such rare-earth perovskite-type gallates, PrGaO₃ is outstanding. Our recent studies of the PrGaO₃ structure using high-resolution powder diffraction techniques and synchrotron radiation revealed negative thermal expansion in the temperature range 12 - 80 K. Nevertheless, no negative expansion could be seen in isostructural LaGaO₃, CeGaO₃ and NdGaO₃.
Considering the structure of RGaO₃ (R=La-Nd) and its solid solutions R_1-xR_xGaO₃ allows us to conclude that many of such compositions are promising candidates for negative expansion at low temperatures. This is because a significant contribution of the overall thermal expansion is caused by rotations of the GaO₆-octahedra. There is, however, a subtle balance between the rotations and distortions of the polyhedra. The negative thermal expansion of PrGaO₃ seems to be related to the violation of this balance caused by interactions between octahedral rotational modes and Pr-ion excitations.
Negative thermal expansion has also been observed in Pr-containing solid solutions (La_0.19Pr_0.81GaO₃, La_0.4Pr_0.6GaO₃) [Aleksiyko et al]. Hence, we performed semiclassical simulations of the thermal expansion of PrGaO₃ using the GULP code based on pairwise interactions. We did, however, not observed traces of negative expansion, which indicates possible electronic effects involved in the nature of such negative thermal expansion of Pr-containing rare-earth gallates.

This work was supported by WTZ (UKR-012-97),UMS (M/85-2003) and PCSR (N7 T08A 00520).

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Origin of the negative thermal expansion in perovskite-type PrGaO3

Presentation: poster at E-MRS Fall Meeting 2004, Symposium H, by Anatoliy Senyshyn See On-line Journal of E-MRS Fall Meeting 2004 Submitted: 2004-05-04 12:26 Revised: 2009-06-08 12:55

Origin of the negative thermal expansion in perovskite-type PrGaO₃

Presentation: poster at E-MRS Fall Meeting 2004, Symposium H, by Anatoliy Senyshyn
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-05-04 12:26 Revised: 2009-06-08 12:55