Journal of Physics and Chemistry of Solids 67 (2006) 1660–1667 High pressure X-ray diffraction study of CdAl 2 Se 4 and Raman study of AAl 2 Se 4 (A ¼ Hg, Zn) and CdAl 2 X 4 (X ¼ Se, S) S. Meenakshi a , V. Vijyakumar a , B.K. Godwal a , A. Eiﬂer b , I. Orgzall c,1 , S. Tkachev c , H.D. Hochheimer c,Ã a Purnima Labs, High Pressure Physics Division, Bhabha Atomic Research Center, Mumbai 400 085, India b Klebendorfer Strasse 47a, D-04425 Taucha, Germany c Department of Physics, Colorado State University, Fort Collins, CO 80523, USA Received 11 January 2006; received in revised form 17 February 2006; accepted 23 February 2006 Abstract We report the results of an X-ray diffraction study of CdAl 2 Se 4 and of Raman studies of HgAl 2 Se 4 and ZnAl 2 Se 4 at room temperature, and of CdAl 2 S 4 and CdAl 2 Se 4 at 80 K at high pressure. The ambient pressure phase of CdAl 2 Se 4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A ﬁt of the volume pressure data to a Birch–Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at 9 GPa is about 10%. The analysis of the Raman data of HgAl 2 Se 4 and ZnAl 2 Se 4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order–disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl 2 S 4 and CdAl 2 Se 4 , which shows a very weak temperature dependence of the Raman-active phonon modes. r 2006 Elsevier Ltd. All rights reserved. Keywords: A. Inorganic compounds; C. High pressure; C. Raman spectroscopy 1. Introduction Contrary to the chalcopyrite (CP) materials with the chemical formula A I B III X 2 VI the ternary adamantine semiconductors with the chemical formula A II B 2 III X 4 VI crystallize in the defect CP (DC) tetragonal or in the defect famatinite (DF) structure. Furthermore, the DC and DF structures contain a crystallographically ordered array of vacancies (stoichiometric voids or vacancies) in the cation sublattice, causing a low packing density of the materials. DC semiconductors have a high potential for optoelec- tronic applications due to their high nonlinear suscept- ibility, optical activity, intense luminescence, and high photosensitivity. In particular, tunable ﬁlters based on CdGa 2 S 4 and UV photodetectors based on CdAl 2 S 4 are already used as devices [1,2]. Pressure induced phase transitions in A I B III X 2 VI CPs have been studied intensively [3,4]. However, the number of high pressure studies on defective A II B 2 III Q 4 VI compounds is rather small [3–10]. In addition, it has been pointed out [5], that further investigations of DC and DF materials under pressure could be of interest for establishing a general systematic of pressure induced phase transitions in these materials. It has been demonstrated that Raman scattering is an excellent tool to study the sequence of pressure induced phase transitions in these materials [5,7,8,10]. When pressure is applied the ordered DC structure undergoes an order–disorder phase transition in the cation sublattice. This transition occurs in two stages as predicted by Bernard and Zunger [11]. In the ﬁrst stage, A and B cations substitute each other leading to a partially cation disordered phase. In the second stage, mutual disorder of ARTICLE IN PRESS www.elsevier.com/locate/jpcs 0022-3697/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2006.02.015 Ã Corresponding author. Tel.: +1 970 491 6246; fax: +1 970 491 7947. E-mail address: dieter@lamar.colostate.edu (H.D. Hochheimer). 1 On leave from: Institute for Thin Film and Microsensoric Technology, Kantstrasse 55, D-14513 Teltow, Germany.