Indian J. Phys. 84 (9) 1223-1228 (2010) © 2010 IACS *Corresponding Author Growth and dc conductivity studies of tripotassium sodium dichromate single crystal Georgekutty Joseph 1 , A Santhosh Kumar 2 , Rajesh R 3 and Godfrey Louis 2* 1 Department of Physics, Sacred Heart College, Thevara, Cochin-682 013, Kerala, India 2 Department of Physics, Cochin University of Science and Technology, Cochin-682 022, Kerala, India 3 School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam-686 560, Kerala, India E-mail : godfrey@cusat.ac.in Received 25 February 2010, accepted 4 May 2010 Abstract : DC electrical conductivity studies were carried out along the three crystallographic axes for tripotassium sodium dichromate (K 3 Na(CrO 4 ) 2 or KNCr). Earlier studies of phase transition in this crystal show successive phase transitions at 239 K and 853 K. In this paper we report the dc electrical conductivity measurements in the temperature region 303–430 K along the crystallographic axes. An anomaly in conductivity was obtained around 326 K along both the axes. This may be attributed as due to a newly observed phase transition in the crystal. DSC taken for the sample also shows exothermic peak supporting the occurrence of newly observed phase transition. Keywords : Glaserite crystals, dc conductivity, phase transition. PACS Nos. : 72.00, 77.80.Bh, 81.10.Dn 1. Introduction Tripotassium sodium dichromate (K 3 Na(CrO 4 ) 2 or KNCr) is a member of a family which can be described by the chemical formula A 3 C(BX 4 ) 2 , where A, C = Na, K, Rb and BX 4 = SO 4 , SeO 4 , CrO 4 and MoO 4 [1]. Experimental studies of these materials show that K 3 Na(SO 4 ) 2 , K 3 Na(CrO 4 ) 2 and K 3 Na(SeO 4 ) 2 undergo ferroelastic phase transitions from a point group m 3 1 to 2/m at about 70 K, 239 K and at 346 K, respectively [2– 4]. In addition to the second-order phase transition at 239 K, KNCr exhibits another structural phase transition at 853 K [3]. The ferroelastic phase transition of KNCr is accompanied by shifts of two crystallographically independent K + cations, as well as by shift and tilting of [CrO 4 ] 2– [5]. Mroz et al [6] performed Brillouin scattering studies and proposed a Landau model to provide a qualitative description of the ferroelastic