Large colored β-Si3N4 single crystals were successfully grown from a Si melt in N2. The transmission optical absorption of coloring β-Si3N4 single crystal shows that impurities introduce a midgap level of ∼2.4 eV into the wide band gap of ∼5.3 eV in nondoped Si3N4. The infrared transmission spectrum and electron probe x-ray microanalysis of β-Si3N4 samples show that the solution of the Al element affects the silicon–nitrogen molecular vibration and the states within the band gap of β-Si3N4. The obtained results mean that the Al impurity acts as the radiative center and is the origin of the color in the β-Si3N4 single crystal.

Si3N4 with high thermal conductivity (120 W/(m.K)) was developed by promoting grain growth and selecting a suitable additive system in terms of composition and amount. β‐Si3N4 doped with Y2O3‐Nd2O3 (YN system) or Y2O3‐A12O3 (YA system) was sintered at 1700°‐2000°C. Thermal conductivity increased with increased sintering temperature because of decreased two‐grain junctions, as a result of grain growth. The effect of the additive amount on thermal conductivity with the YN system was rather small because increased additive formed multigrain junctions. On the other hand, with the YA system, thermal conductivity considerably decreased with increased additive amount because the aluminum and oxygen in the YA system dissolved into β‐Si3N4 grains to form a β‐SiAlON solid solution, which acted as a point defect for phonon scattering. The key processsing parameters for high thermal conductivity of Si3N4 were the sintering temperature and additive composition.

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Low temperature dielectric properties of YMn 0.95 Ru 0.05 O 3 AIP Conf. Correlation between high ionic conductivity and twin structure of La 0.95 Sr 0.05 Ga 0.9 Mg 0.1 O 3 − δ Nature of small-polaron hopping conduction and the effect of Cr doping on the transport properties of rare-earth manganite La 0.5 Pb 0.5 Mn 1−x Cr x O 3In order to identify the carrier responsible for the electrical transport at room temperature in LiMn 2 O 4 from the viewpoint of practical applications as a cathode material, the bulk conductivity measurements by complex-plane impedance analyses have been carried out on LiMn 2 O 4 , Li 0.95 Mn 2 O 4 , and LiMn 1.95 B 0.05 O 4 ͑BϭAl 3ϩ or Ga 3ϩ ͒ together with the measurements of four-probe dc conductivities and dielectric relaxation processes, because these are two candidates for the carrier, a Li ion or a nonadiabatic small polaron of an e g electron on Mn 3ϩ . The comparison of the ionic conductivity estimated numerically from the parameters obtained experimentally for the Li-diffusion in LiMn 2 O 4 with the bulk conductivity indicates that the Li-diffusion seems difficult to play the primary role in the electrical conduction. Instead, a hopping-process of nonadiabatic small polarons of e g electrons is likely to dominate predominantly the electrical transport properties. The dielectric relaxation process, and the activation energies and the pre-exponential factors of the bulk conductivities in Li 0.95 Mn 2 O 4 and LiMn 1.95 B 0.05 O 4 are explained self-consistently in terms of the polaronic conduction.

The thermal conductivity of silicon nitride prepared with varying sintering additive compositions was studied. Samples of Si3N4 + 0.5 mol% Y2O3 + 0.5 mol% Nd2O3 and a further additional agent were gas pressure sintered at 2173 K. MgO or Al2O3 was employed as the additional agent. While both agents improved sinterability, the former promoted grain growth and the latter suppressed it. Thermal conductivity increased with increasing MgO content, and a maximum value of 128 Wm-1 K-1 was attained when 2 mol% MgO was added. In contrast, addition of Al2O3 degrades thermal conductivity. This is probably due to the suppression of grain growth and the dissolution of Al2O3 into Si3N4 grains.