INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 15 (2003) 8315–8326 PII: S0953-8984(03)66393-9 Cation-size control of structural phase transitions in tin perovskites Elizabeth H Mountstevens 1,2 , J Paul Attfield 2 and Simon A T Redfern 1 1 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK 2 Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK Received 18 July 2003 Published 25 November 2003 Online at stacks.iop.org/JPhysCM/15/8315 Abstract The structural evolution at 300 K of the series Sr x Ba 1-x SnO 3 and Sr x Ca 1-x SnO 3 at x = 0.2 intervals has been determined by powder neutron diffraction. All Sr x Ca 1-x SnO 3 samples (x = 0–1) have the Pbnm superstructure. In the series Sr x Ba 1-x SnO 3 , the x = 1.0 and 0.8 samples have the Pbnm superstructure. The x = 0.6 sample has a second orthorhombic structure with space group Imma . There is a tetragonal I 4/ mcm phase at x = 0.4 and the undistorted cubic Pm ¯ 3m structure for x = 0.2 and BaSnO 3 . The octahedral tilt angles show a smooth variation with average A cation radius over the range of superstructures described by mean field theory close to the transition. The transitions are also analysed via the variation of spontaneous strains. 1. Introduction The alkaline earth stannates, ASnO 3 (A = Ca, Sr, Ba), have recently been investigated as potential capacitor components with a small temperature coefficient of capacitance [1]. Stannates form solid solutions with barium titanate and when added in small quantities will lower the temperature of the ferroelectric transition [2]. SrSnO 3 has been studied as a high temperature humidity sensor and is especially effective when doped with La 3+ [3]. Recently there has also been interest in the alkaline earth stannates as nitrogen oxide absorbers in lean exhaust gases [4]. The nitrogen oxide gases are trapped on a selective adsorbent such as the stannates and then reduced using a small burst of fuel or recirculated to the engine to be thermally destroyed. BaSnO 3 shows particular promise as a selective adsorbant. All of the alkaline earth stannates have perovskite structures. CaSnO 3 is orthorhombic at room temperature with the common √ 2a × √ 2a × 2a Pbnm superstructure of the ideal perovskite cell (cubic parameter a ) [5]. SrSnO 3 was originally thought to have a doubled cubic structure with 8 formula units per unit cell [6]. More recently, however, powder neutron diffraction has shown SrSnO 3 also to have the orthorhombic Pbnm structure [7]. BaSnO 3 0953-8984/03/498315+12$30.00 © 2003 IOP Publishing Ltd Printed in the UK 8315