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We present temperature-dependent refractive index along crystallographic b[010] and a direction perpendicular to (100)-plane for monoclinic phase (β) Ga(2)O(3) single crystal grown by the optical floating zone technique. The experimental results are consistent with the theoretical result of Litimein et al.1. Also, the Sellmeier equation for wavelengths in the range of 0.4-1.55 μm is formulated at different temperatures in the range of 30-175 °C. The thermal coefficient of refractive index in the above specified range is ~10(-5)/°C.

We report coexistence of high spin Co3+ and Co2+ in ceramic Co3TeO6 using X-ray Absorption Near Edge Structure (XANES), DC magnetization, and first principles ab-initio calculations. The main absorption line of cobalt Co K-edge XANES spectra, along with a linear combination fit, led us to estimate relative concentration of Co2+ and Co3+as 60:40. The pre edge feature of XANES spectrum shows crystal field splitting of ∼1.26 eV between eg and t2g states, suggesting a mixture of high spin states of both Co2+ and Co3+. Temperature dependent high field DC magnetization measurements reveal dominant antiferromagnetic order with two Neel temperatures (TN1 ∼ 29 K and TN2 ∼ 18 K), consistent with single crystal study. A larger effective magnetic moment is observed in comparison to that reported for single crystal (which contains only Co2+), supports our inference that Co3+ exists in high spin state. Furthermore, we show that both Co2+ and Co3+ being in high spin states constitute a favorable ground state through first principles ab-initio calculations, where Rietveld refined synchrotron X-ray diffraction data are used as input.

We report the effect of annealing atmosphere on structure and magnetic and dielectric properties of double perovskite-type EuCo0.5Mn0.5O3 (ECMO). Polycrystalline samples prepared by high-temperature reaction were subjected to annealing in different oxygen partial pressures and investigated by powder X-ray diffraction, magnetometry, and ac impedance spectroscopy. While the samples annealed in air or oxygen environment were found to have cation-disordered orthorhombic structure (Pnma), the samples annealed in inert atmosphere have Eu3+ deficient perovskite-type structure. The temperature- and field-dependent magnetizations indicate the ferromagnetic transition around 130 K. The differences in field-cooled and zero-field-cooled magnetization and significant effect of magnetic field on magnetic properties suggest metamagnetic behavior in ECMO. Randomly distributed clusters of ferromagnetically (FM) and antiferromagnetically (AFM) paired magnetic ions and their relative proportions are reflected in their magnetic properties. The weak nature of the antiferromagnetic interactions is reflected in the switching of AFM to FM state at appreciably lower field strength (∼300 Oe). Dielectric measurements indicate that the samples annealed in air or oxygen show large dielectric permittivity (≥2000) compared to that in inert atmosphere (∼400). The analyses of temperature- and frequency-dependent loss tangent and modulus data revealed two different types of relaxations which possibly originate from two polaronic conduction processes.