Low-temperature structural properties of orthorhombic TbAlO3, TmAlO3 and LuAlO3 perovskites

Dmytro M. Trots 1,2Leonid Vasylechko 3Anatoliy Senyshyn 2,3Tadeusz Łukasiewicz 4

1. Hamburger Synchrotronstrahlungslabor HASYLAB, Notkestrasse 85, Hamburg 22607, Germany
2. Technische Universität Darmstadt, Institute of Materials Science, Petersenstr. 23, Darmstadt 64287, Germany
3. Lviv Polytechnic National University, 12 Bandera, Lviv 79013, Ukraine
4. Institute of Electronic Materials Technology (ITME), Wólczyńska 133, Warszawa 01-919, Poland

Perovskite type TbAlO3 and LuAlO3 rare-earth aluminates attract considerable interest as laser media [1,2]. This work is a continuation of our systematic studies on the crystal structure of perovskite type rare-earth aluminates and gallates. Here we report structural investigations on TbAlO3, TmAlO3 and LuAlO3 at low temperatures using high-resolution synchrotron powder diffraction performed at beamline B2 (HASYLAB/DESY). All three compounds possess the GdFeO3 type of structure (space group Pbnm) in the whole temperature range studied (20-300 K) and exhibit quite various thermal behaviours of the lattice parameters.
The thermal dependencies of the lattice parameters of LuAlO3 display a rather typical (nonlinear and smooth) increase with temperature, whereas the behaviour of TmAlO3 shows deviations from a “normal” law which are reflected in a “sigmoid” expansion of the lattice along the [100] direction. Unusual trends occur in the thermal behaviour of TbAlO3: at T~60 K all three unique elements of the thermal expansion tensor undergo the zero value which is indicated by the observed extrema on the thermal dependencies of the respective lattice parameters. The thermal expansion coefficient in the [100] direction of the perovskite cell α11 achieves one more negative minimum around 130 K and then increases through the zero value (ca. 200 K). The observed smooth and nonlinear increase of the lattice dimensions in LuAlO3 and the anomalous thermal behaviour occurred in TbAlO3 and TmAlO3 can be associated to interactions between phonons and the electron subsystem of rare-earth ions with open f-shell [3].

We are indebted to Andreas Berghaeuser for his help with maintenance of cryostat.
[1] Sardar et al., J APPL PHYS 100 (2006) 083108
[2] Drozdowski et al., NUCL INSTRUM METH A 562 (2006) 254
[3] Vasylechko et al., Handbook on the Physics and Chemistry of Rare-earths, ed. K. Gschneidner, J. Bunzli, and V. Pecharsky (Elsevier, Amsterdam), 39 (2008) in print

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Presentation: Poster at 11th European Powder Diffraction Conference, Poster session, by Dmytro M. Trots
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-04-28 18:18
Revised:   2009-06-07 00:48
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