TITLE:
Electron Paramagnetic Resonance Studies of Cu2+ and VO2+ Spin Probes in RO-Li2O-Na2O-K2O-B2O3 (R = Zn, Mg, Sr and Ba) Glass Systems
AUTHORS:
Abdul Hameed, Gokarakonda Ramadevudu, Siddey Laksmisrinivasa Rao, Mohmmad Shareefuddin, Mudumba Narasimha Chary
KEYWORDS:
Borate Glasses; Electron Paramagnetic Resonance (EPR); Optical Absorption; Spin-Hamiltonian Parameters
JOURNAL NAME:
New Journal of Glass and Ceramics,
Vol.2 No.1,
January
12,
2012
ABSTRACT: Mixed alkali and alkaline earth oxide glasses of RO-Li2O-Na2O-K2O-B2O3(R = Zn, Mg, Sr and Ba) system were studied by electron paramagnetic resonance (EPR) and optical absorption spectroscopy. Cu2+ and VO2+ ions were used as the spin probes. The glasses containing 1 mole% of Cu2+ and 2mole% of VO2+ were prepared by the melt quenching method. X-ray diffraction studies of the samples did not reveal crystalline phases. EPR measurements were made at X-band frequencies with 100 kHz field modulation, at 310 K. Optical spectra were recorded in the wavelength range 300 nm - 800 nm. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values in the case of Cu2+ indicated that the ground state of Cu2+ was orbital (2B1g) and the site symmetry around Cu2+ is tetragonally distorted octahedral. The variation of gll and All with the alkaline earth oxide (RO) composition was found to be non-linear which may be due to the change in the ligand field strength at the site of Cu2+ ions. From the spin-Hamiltonian parameters of VO2+, it was observed that the vanadyl ions exist as VO2+ ions in octahedral coordination with tetragonal compression and have C4V symmetry with ground state dxy. Tetragonality (△gll/△g) of V4+ ion sites exhibited non-linear variation with RO content, which indicated change in the ligand field at the site of V4+. A broad optical absorption band was observed in the glass containing Cu2+ ions corresponding to the 2B1g → 2B2g transition. From the EPR and optical data the bond parameters were evaluated. In the case of VO2+ ions, the covalency rates were estimated.