IOP PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 19 (2007) 226206 (8pp) doi:10.1088/0953-8984/19/22/226206 Disorder-induced Raman scattering in rhenium trioxide (ReO 3 ) J Purans 1,2 , A Kuzmin 2 , E Cazzanelli 3 and G Mariotto 1 1 Dipartimento di Fisica, Universit` a di Trento, I-38050 Povo (Trento), Italy 2 Institute of Solid State Physics, University of Latvia, Kengaraga street 8, LV-1063 Riga, Latvia 3 LICRYL-CNR and CEMIF.CAL, Dipartimento di Fisica, Universit` a della Calabria, I-87036 Arcavacata di Rende (Cosenza), Italy E-mail: xas@latnet.lv (J Purans) and a.kuzmin@cfi.lu.lv Received 29 January 2007, in final form 29 March 2007 Published 3 May 2007 Online at stacks.iop.org/JPhysCM/19/226206 Abstract Raman scattering in cubic metallic perovskite (ReO 3 ) was studied at room temperature for well-crystallized monolith, polycrystalline powder and thin film samples. Defect-induced first-order Raman scattering was detected from the sub-surface region, given by the penetration depth of a 633 nm laser, and its origin was explained on the basis of a rigid-ion vibrational model for bulk ReO 3 . A quenching of the Raman intensity was observed in crystalline monolithic ReO 3 upon increasing the temperature up to 250 ◦ C and was related to crystal surface reconstruction/annealing. 1. Introduction Transition metal oxides (TMOs) constitute a very interesting class of materials because of the variety of functional properties and phenomena exhibited by them. Among different TMOs, rhenium trioxide (ReO 3 ) [1] is known for its unexpectedly high electrical conductivity similar to that of copper, therefore it is often referred as a ‘covalent metal’ [2–5]. ReO 3 is also unusual in that the cubic perovskite-type structure (ABO 3 ) is non-distorted at atmospheric pressure at all temperatures [1, 6]. The empty A sites permit wide librational motions of the ReO 6 octahedra, resulting in an enhanced compressibility and ultra low or negative thermal expansion [7]. In contrast to ReO 3 , tungsten trioxide WO 3 as well as many perovskites, like SrTiO 3 , BaTiO 3 and KNbO 3 , show the condensation of one or more optical modes causing the rearrangement of the local electronic and atomic structure and related structural phase transitions [8]. In spite of the fact that cubic ReO 3 is widely used as a model of an ideal perovskite structure, only a few theoretical works have so far been devoted to the investigation of its vibrational properties [9–11]. The common feature for all previous works is the prediction of high-frequency modes occurring at the Brillouin zone centre (Ŵ point) at 700–1000 cm −1 0953-8984/07/226206+08$30.00 © 2007 IOP Publishing Ltd Printed in the UK 1