Electron Spin Resonance of Cr³⁺ in K_1–xTl_xAl(SO₄)₂ · 12 H₂O

Abstract

The electron spin resonance (ESR) of Cr 3+ in K 1−x Tl x Al(SO 4 ) 2 ·12H 2 O has been studied at 300 K and 9.45 GHz. The ESR spectrum for x between 30 and 90% shows several chromium complexes. The variation of the zero-field splitting parameter D suggests that monovalent ions play an important role in the trigonal distortion of the water octahedron around the trivalent metal ion in alums. O (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 T h 6 (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 Al 3+ has six water ExperimentalSingle crystals of PTA (x = 0 to 1) were grown at ∼ 300 K by slow evaporation of the saturated aqueous solutions of appropriate metal sulphates. Cr 3+ was introduced into the host lattice by adding chromic sulphate (1% by weight). The ESR experiments were performed on a JEOL FE-3X homodyne spectrometer operating at ∼ 9.45 GHz equipped with a TE 011 cylindrical cavity and 100 kHz field modulation. A speck of powdered diphenyl picrylhydrazil (DPPH) used as a field marker (taking g DPPH = 2.0036) was inserted simultaneously into the sample cavity. The crystals were mounted on quartz rods. The angular variation studies were made using a JES-UCR-2X sample angular rotating device. Powder spectra were recorded from powder in quartz tubes. Each powdered ESR sample was obtained by grinding an individual untwinned crystal.For an arbitrary orientation of the crystal, the ESR spectrum consists of a number of intense lines besides some weak lines on the low magnetic field side of the spectrum in all the crystals studied. For x = 0