JOURNAL OF RAMAN SPECTROSCOPY J. Raman Spectrosc. 2005; 36: 83–88 Published online 7 December 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jrs.1271 Short Communication Lattice dynamic investigation of the Raman and infrared wavenumbers of orthorhombic R 2 BaCuO 5 (R = Y, Ho, Gd) oxides H. C. Gupta * and Vikas Sharma Physics Department, Indian Institute of Technology, Hauz Khas, New Delhi-110016, India Received 3 July 2004; Accepted 25 September 2004 A short-range force constant model was applied for the first time to investigate the Raman and infrared wavenumbers in R 2 BaCuO 5 (R = Y, Ho, Gd) oxides in their orthorhombic phase of space group Pnma. Calculations of zone center phonons were made with 17 stretching and four bending force constants. The force constants were evaluated using the electronegativities and the atomic distances. The calculated values of Raman wavenumbers are in reasonable agreement with the available observed values. The infrared wavenumbers were assigned for the first time. Copyright  2004 John Wiley & Sons, Ltd. KEYWORDS: phonons; lattice dynamics; green phase; non-superconducting oxides INTRODUCTION Mixed oxides of stoichiometry R 2 BaMO 5 (R D trivalent lanthanide or yttrium, M D Cu, Co, Ni) have attracted great interest since the beginning of the last decade owing to their relation with high-temperature superconducting materials. 1 Further, these oxides present different crystallographic structures depending on M and the radius of R. 2 Most of the compounds with M D Cu were formed as by-products or impurities during the synthesis of RBa 2 Cu 3 O 7 -type high-T c superconductors. 3 The study of these impurities, also called ‘green phases’, of composition R 2 BaMO 5 will provide a deeper insight into the relevant physicochemical properties of the R–Ba–Cu–O system. The study of the Raman and infrared spectra of these impurity ‘green phases’ will be useful from the point of view of both structural properties and the relation to superconducting properties. Hence for the first time, in this work, an attempt was made using normal coordinate analysis to investigate the zone center wavenumbers of R 2 BaCuO 5 (R D Y, Ho, Gd) in their orthorhombic structure. For a rigorous and systematic treatment, the interatomic force constants were evaluated using the relation between the force constants and the electronegativities as given by Eldridge and Bates. 4 L Correspondence to: H. C. Gupta, Physics Department, Indian Institute of Technology, Hauz Khas, New Delhi-110016, India. E-mail: hcgupta@physics.iitd.ernet.in A total of 21 interatomic force constants, 17 stretching and four bending, were utilized to obtain reasonable agreement between the theoretical and experimental Raman wavenumbers. The infrared wavenumbers were assigned for the first time. STRUCTURE AND SYMMETRY COORDINATES Orthorhombic R 2 BaCuO 5 (R D Y, Ho, Gd) crystallizes in Pnma space group (No. 62, D 2h 16 ). 5 The primitive cell contains four formula units and the structure is shown in Fig. 1. The Cu atoms are surrounded by five oxygen atoms forming twisted quadratic pyramids, the R atoms occupy two different sites in an environment of seven oxygen atoms and the Ba atoms sit in a complex 11 oxygen atom environment. The RO 7 trigonal prisms form distorted chains parallel to the y-axis. The oxygen atoms occupy three different sites and two-thirds of them form two types of chains extended along the z-axis. The site symmetry, the atomic coordinates 5 and the phonon contribution at the  point in the case of R 2 BaCuO 5 are given in Table 1. The total number of zone center modes present for each species of the space group is  D 16A g C 11B 1g C 16B 2g C 11B 3g C 11A u C 16B 1u C 11B 2u C 16B 3u Further, of these 108 normal modes, 16A g , 11B 1g , 16B 2g and 11B 3g are Raman active, B 1u , B 2u and B 3u are acoustic modes Copyright  2004 John Wiley & Sons, Ltd.