Journal of Solid State Chemistry 178 (2005) 270–278 Crystal structure and thermal expansion of PrGaO 3 in the temperature range 12–1253K L. Vasylechko a,Ã , Ye. Pivak a , A. Senyshyn a , D. Savytskii a , M. Berkowski b , H. Borrmann c ,M.Knapp d , C. Paulmann e a Institute of Telecommunications, Radioelectronics and Electronics Technique,‘‘Lviv Polytechnic’’ National University, 12 Bandera St., UA-79013 Lviv, Ukraine b Institute of Physics Polish Academy of Sciences, Al. Lotniko´w 32/46, 02-668 Warsaw, Poland c Max-Planck-Institut fu¨r Chemische Physik fester Stoffe, No¨thnitzer Strasse 40, D-01187 Dresden, Germany d Institute for Materials Science, Darmstadt University of Technology, Petersenstrasse 23, D-64287 Darmstadt, Germany e Mineralogisch-Petrographisches Institut, Universita¨t Hamburg, Grindelallee 48, D-20146 Hamburg, Germany Received 20 August 2004; received in revised form 29 September 2004; accepted 4 October 2004 Abstract CrystalstructureandthermalexpansionofPrGaO 3 singlecrystal,obtainedbytheCzochralskymethod,havebeeninvestigatedby means of single crystal and high-resolution powder diffraction techniques applying synchrotron radiation in a wide temperature range12–1253K.ItwasshownthatPrGaO 3 adoptsanorthorhombicallydistortedvariantofperovskitestructure(GdFeO 3 typeof structure, space group Pbnm, Z ¼ 4) throughout the entire temperature range. Temperature dependence of lattice parameters and respectiveunitcellvolumedisplayanisotropicandnonlinearbehavior.Latticecontractionin[010]-and[100]-directionsisobserved in temperature ranges 12–180 and 12–50K, respectively. In total PrGaO 3 exhibits a negative thermal expansion of the volume between12and50K.Alinearincreaseoftheaveragebondlengths(PrO) 8 , (PrO) 9 , (PrO) 12 , (GaO) 6 ,aswellastheaverage(OO) 8 distanceswasobserved.However,withtheaverage(PrPr) 6 ,(PrGa) 8 and(GaGa) 6 cation–cationdistancesachangeofslopeoccurs at200–300K.Overall,withrisingtemperatureadecreaseofthedeformationisobservedfortheperovskitetypestructure.Aphase transition from orthorhombic to rhombohedral structure of PrGaO 3 around 1855K is predicted from extrapolation of both the temperature dependencies of the (PrPr) 6 /(GaGa) 6 distance ratio and of the experimental temperatures of the R ¯ 3c–Pbnm phase transition for LaGaO 3 , CeGaO 3 and La 1x RE x GaO 3 (RE—rare earth) perovskites. r 2004 Elsevier Inc. All rights reserved. Keywords: PrGaO 3 ; Single crystal; Perovskite; Crystal structure; Negative thermal expansion; Phase transition; Synchrotron radiation 1. Introduction Rare-earthgallates,duetotheirparticularproperties, havefoundwideapplicationindifferentareasofscience and engineering. In particular, NdGaO 3 , LaGaO 3 , PrGaO 3 as well as respective solid solutions are used as substrate materials for epitaxial growth of high- temperature superconductors (HTSC), collosal magne- toresistive films and for GaN film deposition [1–6].A small lattice mismatch, similar coefficients of thermal expansion, high thermal and chemical stability, and in particular only small misfits at epitaxial growth tem- peraturesareall-importantfeaturesingrowinglayersof HTSC materials. Recently, it was reported [7–10], that lanthanum, neodymium and praseodymium gallates, dopedwithstrontiumandmagnesiumshowhighoxygen ion conductivity at temperatures of about 870–1070K, and are considered as prospective solid electrolytes for the application in solid oxide fuel cells (SOFCs). At ambient temperatures PrGaO 3 adopts an orthor- hombically distorted GdFeO 3 -type structure (space ARTICLE IN PRESS www.elsevier.com/locate/jssc 0022-4596/$-see front matter r 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jssc.2004.10.005 Ã Corresponding author. Fax: +38322742164. E-mail address: crystal-lov@polynet.lviv.ua (L. Vasylechko).