Chandra P. Khattak

Effect of gadolinium substitution on the linear thermal expansion of barium sodium niobate

Abstract Ba2NaNb5O15 (BSN) exhibits a large thermal contraction in its c-axis between 350° and 750°C. This behaviour contributes to a serious cracking problem during its crystal growth. The substitutions of Gd for Ba and/or Na in BSN can be made with either anion or cation compensation. The former, namely, type A, compositions were found to eliminate the thermal contraction behaviors, and had small variations in their linear thermal expansion coefficients, α, between 50° and 650°C. With good ferroelectric and dielectric properties, they showed potentials to replace the BSN crystal in electro-optic devices.

Refinements in the determination of minority-carrier diffusion length measurements of polycrystalline silicon materials by the surface photovoltage method

The microstructures of polycrystalline silicon samples show significant differences in their absorption coefficients within the range of wavelength of interest for the surface photovoltage (SPV) method. The accuracy in the determination of the minority‐carrier diffusion length of polycrystalline materials by the SPV method was demonstrably improved with the use of the determined absorption coefficients for each individual sample.

Compositional variations in ternary superconductor alloys of Nb3GexAl1−x

Abstract Metallurgical specimens of ternary Nb 3Ge x Al 1− x ( x in the range 0.18–0.28) alloys after heat treatment showed large compositional variations within each specimen. Such variations can be grouped into two compositional regions in the ternary diagram for each specimen. They provide an explanation for the close agreement in the superconducting transition temperatures for this series of alloys.

Effect of non-isoelectronic cation substitution on lattice parameters of barium sodium niobate

Ceramic samples of Ba2 NaNb5O15, with the cations selectively substituted by Gd or Cr, showed that the changes in their orthorhombic lattice parametersa, b, andc were linearly correlated to each other. The changes in lattice parameters in thea, b, andc directions occurred proportionally in the ratio of 2.5∶3.27∶1.0.

Cause of discrepancies in diffusion coefficient data as obtained from the sintering experiments of oxides

Abstract It is shown that when the distribution of particle sizes is included, the calculated diffusion coefficient value from the sintering experiment can be many orders of magnitude greater than the usual calculated value which was based on an average particle size.

Non-linear magnetoelectric effect in Cr2O3 crystals

Abstract The dielectric constant (K′) of Cr2O3 crystals has been measured under orthogonal E and H fields. The change in K′ due to the fields shows a non-linear magneto-electric effect in the neighbourhood of the Neel point T N. The effect can be explained in terms of antiferromagnetic domains.