Electron Spin Resonance of VO2+ in LiKSO4 Single Crystals

Lithium potassium sulfate, LiKSO4, belongs to the family of compounds LiMAB4 (M=Na,K,Rb,Cs,NH4; AB4=SO4,BeF4). LiKSO4 has been investigated in great detail because of its large variety of physical properties found in different structural phases [1, 2]. This paper reports the electron spin resonance (ESR) of vanadyl, VO, ion impurities in single crystals of LiKSO4 at 295 K. The crystal structure of LiKSO4 at 295 K is hexagonal with space group P63 [3, 4]. The unit cell has the dimensions a = 0.5146 nm, c = 0.8636 nm and contains two formula units [4]. The potassium atoms occupy positions on the hexagonal c-axis. They are coordinated by nine oxygens. The Li atoms are coordinated with four oxygens. Single crystals of LiKSO4, doped with VO, were grown at ∼ 300 K by slow evaporation of an aqueous solution containing an equimolar mixture of corresponding sulfate to which 0.5 wt % VO was added. The crystal grows in flat hexagonal plates, the plane of which is perpendicular to the c-axis. The ESR experiments were performed with a JEOL FE-3X homodyne spectrometer operating at ∼ 9.45 GHz, equipped with a TE001-cylindrical cavity and 100 kHz field modulation. A speck of powdered DPPH used as a field marker (taking gDPPH = 2.0036) was inserted simultaneously into the sample cavity. The angular variation studies were done using a JES-UCR-2X sample angular rotating device. Powder spectra were recorded by powder in quartz tubes. The powder ESR samples were obtained by grinding an individual crystal. For an arbitrary orientation of the crystal, the ESR spectrum of the vanadyl ions consists of a large number of resonance lines. In addition to weak lines from