G. Sivarama Sastry

Covalency effects on the E.S.R. spectra of VO2+ in hexaaquo magnesium dihydrogen ethylenediaminetetraacetic acid

The E.S.R. spectra of VO2+ doped in hexa-aquo magnesium dihydrogen ethylenediaminetetra-acetic acid and two magnesium Tuttons salts are studied. VO2+ is found to enter the lattice substitutionally into the Mg sites. Only one set of eight lines is observed and transitions due to other orientations of the V-O bond were not observed. The V-O bond is found to coincide with the Mg-O w1 bond direction. The electric field symmetry at the Mg site is found to be rhombic. The Fermi contact term and the bonding coefficient are evaluated from the spin-Hamiltonian parameters and these values, together with the low value of Az , indicate a high degree of covalency in the Mg(H2O)6 octahedron, brought about by the participation of the water molecules in large scale hydrogen bonding.

Proton conduction in (NH4)3 H(SO4)2 single crystals

Abstract D.C. electrical conductivity, DTA and coulometric studies on (NH4)3 H(SO4)2 single crystals are made. Conductivity is markedly anisotropic with maximum along c∗ direction. A sudden jump in the conductivity plot along c∗ direction at 413 K is supported by a large endothermic peak in DTA, confirming the presence of transition at this temperature. The values of activation energy calculated from conductivity measurements indicated that the charge carriers are protons. This was further confirmed by coulometric experiment where the gas evolved was hydrogen, as established by a gas chromatograph and the volume of H2 released agreed with that expected from electrolysis. The mechanism of protonic conduction in this crystal is discussed.

Single crystal ESR study of Cu2+ in diglycine barium chloride monohydrate

ESR studies have been made on Cu2+ doped diglycine barium chloride monohydrate. Two Cu2+ lattice sites, Cu2+(I) and Cu2+(II), have been identified. Cu2+(I) exhibits only one set of four hyperfine lines in all directions and the g and A values show this complex to have a ‖3z2−r2〉 ground state. For the second lattice site, Cu2+ is found to enter into a substitutional Ba2+ site. The spectra for Cu2+(I) and Cu2+(II) lattice sites are found to have intensities in the ratio 10:1 suggesting a preferential occupation of the interstitial position by the Cu2+ ion. The spin Hamiltonian parameters and the molecular orbital coefficients are evaluated for the two sites.

EPR of Mn2+ in cobalt fluosilicate hexahydrate

Abstract The EPR of Mn 2+ in cobalt fluosilicate hexahydrate has been studied at room temperature. An axial spin-hamiltornian explained the observed spectrum. The presence of a single Mn 2+ site in an octahedral oxygen environment was confirmed. A phase transition at −55°C was observed.

Electron spin resonance studies of Cu2+ doped in cadmium maleate dihydrate single crystals

Electron spin resonance studies have been carried out on Cu2+ ion doped in single crystals of cadmium maleate dihydrate at 303 and 77K. It has been found that Cu2+ enters this lattice interstitially. The spin Hamiltonian parameters have been evaluated and the ground state wave function is found to be predominantly |X2 −Y2〉 with a slight admixture of |3Z2 −r2〉.

Calorimetric measurements on Ge-Bi-Se-Te glasses

On presente les resultats de mesures calorimetriques sur des verres Ge 2 0 Bi x Se 70-x Te 10 (x-7, 9, 11 et 13). On etudie les variations de la temperature de transition vitreuse, de la temperature de cristallisation en fonction de la teneur en bismuth

EPR Studies of a structural phase transition in Mn2+-doped zinc fluotitanate hexahydrate

Electron paramagnetic resonance studies of Mn2+ in zinc fluotitanate hexahydrate (ZnTiF6·6H2O) have been made between 77 and 300 K, in the X-band frequency range. At 173±2 K a structural phase transition was observed. The axial symmetry at room temperature with a single magnetic site was destroyed in the low-temperature phase, where two crystallographically inequivalent sites rotated by 8° from the axis could be identified, with their symmetry axis retained along the room-temperature c axis. The important features associated with this phase transition are reported along with the room-temperature data.

Single crystal ESR of VO2+ in hexa‐urea aluminium perchlorate

Electron spin resonance studies have been made on VO2+ in hexa‐urea aluminium perchlorate single crystals and VO2+ is found to take up substitutional Al3+ sites. The V–O bond takes six possible orientations in the lattice and each of these are at 45° to the crystallographic c axis. Molecular orbital coefficients have been evaluated using the spin Hamiltonian parameters and optical absorption data.

Electron spin resonance and optical absorption studies of Cu2+ doped in potassium hydrogen maleate single crystals

Abstract The results of electron spin resonance studies on Cu2+ doped in potassium hydrogen maleate single crystals at 300 K are presented. The spin Hamiltonian parameters evaluated indicate a square planar environment for Cu2+ ion in this lattice. From the crystal structure data and the direction cosines of the principal axes of the g tensor, it is concluded that the Cu2+ ion enters the lattice in an interstitial position. Charge compensation is achieved by the release of protons. Using the optical absorption and ESR data, bonding parameters and orbital reduction factors are also evaluated.

Electrical conductivity and stimulated thermocurrent studies in dicalcium lead propionate single crystal

Electrical conductivity and stimulated thermocurrent (stc) studies are carried out in dicalcium lead propionate (dlp) in pure, Cu2+, Fe3+ and acetate doped single crystals over a temperature range of 303° to 503° K. Conductivity measurements on pure and doped single crystals ofdlp indicate that both propionate anions and metallic cations are responsible for the transition occurring at 333°K. Thermoelectric power measurements from 340° to 500°K indlp (pure) indicate that the transport charge carriers are electrons. A model for the conduction mechanism is proposed on the basis of hopping ofπ or resonating electrons of carboxyl groups through tunnel paths involving metal ions (Pb2+ and Ca2+). From activation energies estimated from conductivity andstc measurements, thestc peak indlp (Fe3+) occurring at 513°K is attributed to impurity vacancy jump mechanism.