Electron Spin Resonance of Cr 3 + in K 1 – x Tl x Al ( SO 4 ) 2 · 12 H

The potassium, ammonium and thallium alums form continuous series of solid solutions. By means of xray diffraction Klug and Alexander [1] have shown that these solid solutions are ideal from the stand point of Vegard’s law [2], particularly solid solutions of ammonium and thallium alum [1]. Jain [3] has studied the electron spin resonance (ESR) of Cr3+ in single crystals of mixed alums of ammonium and thallium and observed the presence of four magnetically inequivalent but otherwise identical Cr3+ complexes (formed by the substitution of Al3+ by Cr3+). The zero-field splitting (ZFS) was found to vary with the composition. Garrett and Boop [4] concluded those from the ESR of powder spectra the presence of other chromium complexes beside those observed by Jain [3]. Chand et al. [5] have studied the ESR of Cr3+ in the mixed alums (NH4)xM1−xAl(SO4)2·12H2O (M=Na,K) and have observed only one kind of chromium complexes. It seemed of interest to investigate the ESR of Cr3+ diluted in K1−xTlxAl(SO4)2·12H2O (PotaniumThallium-Alum = PTA) in order to understand the variation of the ZFS with composition. The ESR of PTA for x = 0 and 1 has been previously studied [6, 7]. The potassium aluminium and thallium aluminium alums which belong to the α type of alum [8, 9], form a continuous series of solid solutions [1, 10]. The alum belongs to the cubic system with space group Th(Pa3). Because of different atomic arrangements they exists in three types, namely α , β , and γ [8]. The K and Tl alum belong to the α type. The lattice constant a of the K alum is 1.2158 nm, and of the Tl alum is 1.2232 nm [9]. The Al3+ has six water