J. Philip

A low loss, dielectric substrate in ZnAl2O4–TiO2 system for microelectronic applications

A temperature stable low loss substrate based on 0.83ZnAl2O4–0.17TiO2 (ZAT) was developed as a substitute to Al2O3 for possible applications in microelectronic industry as substrates and packaging materials. The thermal conductivity of ZAT is 59Wm−1K−1 which is more than twice as that of Al2O3. The thermal-expansion coefficient of this dielectric is 6.3ppm∕°C which is comparable to that of silicon used in microelectronic circuitry. Furthermore, 0.83ZnAl2O4–0.17TiO2 dielectric is chemically inert with silicon, which increases its applicability in microelectronic packages.

Composition dependence of optical band gap and thermal diffusivity of AsTeSe glasses

The composition dependence of the optical band gap, E0, and thermal diffusivity, α, of As Te Se glasses, prepared by the conventional melt-quenching technique, have been determined using photoacoustic technique which is based on the detection of the acoustic signal produced when a modulated light beam is incident on the sample. The optical band gap is found to decrease with increase in As concentration, whereas thermal diffusivity shows a threshold maximum at 40 at.% of As content which is the stoichiometric compositions of the As Te Se system. The observed behaviour is explained on the basis of chemical bonding between the constituents and the idea of rigidity percolation in covalent random networks.

Stability of the ferroelectric phase in polycrystalline KNO3 investigated by photoacoustic and calorimetric techniques

The successive phase transitions in a polycrystalline KNO3 sample have been studied using photacoustic and calorimetric techniques. The measured temperature dependence of the photoacoustic amplitude carries signatures of the transitions undergone by the sample. The results indicate that the intermediate ferroelectric phase in KNO3 is only a metastable one. This raises doubts regarding its applicability in fabricating ferroelectric memory devices.

Optical absorption and thermal diffusivity in GexTe100−x glasses by the photoacoustic technique

Abstract Abstract The variation in the optical energy gap with composition in the GexTe100-x system (15≤x≤28) of glasses in bulk form has been studied using photoacoustic techniques. It is found that the optical energy gap increases with increasing composition factor x, with the rate of increase showing a slowing-down trend for compositions with x > 20. The composition dependence of the thermal diffusivity of these samples has also been measured. The thermal diffusivity is found to peak around the composition corresponding to x = 20. The observed phenomena are explained on the basis of chemical bond formation in this system of glasses. The change in the short-range order and increase in the number of Te-Te bonds with decreasing x are interpreted as being responsible for the behaviour exhibited by these materials.

Thermal properties of glycine phosphite across ferroelectric phase transition: a photopyroelectric study

Abstract A photopyroelectric measurement of the thermal parameters of glycine phosphite (GPI) single crystals across the ferroelectric phase transition temperature has been carried out. The thermal parameters—thermal diffusivity (α), thermal effusivity (e), thermal conductivity (K), and heat capacity (cp)—of GPI single crystals are reported. The para-ferroelectric phase transition is reflected in these thermal parameters as anomalies at the transition point. The anisotropy in thermal wave propagation is established by measuring thermal conductivity along the a, b, and c crystal axes. The anomalous variations in the thermal parameters across the phase transition temperature reveal an order-disorder type transition at 224 K in this crystal.

Elastic properties of zinc tris(thiourea) sulphate single crystals

Zinc tris(thiourea) sulphate (ZTS) single crystals possess excellent nonlinear optical properties and are nearly 1.2 times more efficient than potassium dihydrogen phosphate in optical harmonic generation. Large single crystals of this material have been grown from aqueous solution. All nine second order elastic stiffness constants of this orthorhombic crystal have been determined by measuring the velocity of propagation of ultrasonic waves of longitudinal and transverse polarizations along specific symmetry directions. The McSkimin Δt correction has been applied for better accuracy of velocity values. The corresponding elastic compliance constants and Poisson’s ratios have also been evaluated. Planar plots of phase velocity, group velocity, slowness, Young’s modulus, and linear compressibility have been drawn to display the anisotropy of wave propagation in the crystal. The bulk modulus and volume compressibility of this crystal have been evaluated from the elastic constant data. Variation of a selected ...

Temperature dependence of elastic and dielectric properties of (Bi2O3)1 − x(CuO)x oxide glasses

Oxide glasses with the general formula (Bi2O3)1 - x(CuO)x have been prepared by quick quenching technique. Their longitudinal and shear elastic moduli have been determined by measuring the corresponding ultrasonic wave velocities between 300 and 470 K, which are well below the glass transition temperature of this system. Temperature variation of ultrasonic velocity and attenuation exhibit anomalies around 435 K in glasses with x ≥ 0.3. A nonlinear behaviour is also reflected in the CuO concentration dependent dielectric constant curve around x = 0.3. These anomalies are interpreted in terms of a structural softening (or transformation) taking place in samples having CuO concentration above the critical value. The high dielectric constant of these glasses show very little increase with increase of temperature. Anomalies are also found in the temperature dependence of dielectric constant around 435 K. This behaviour is again considered to be associated with the softening of the glass network.

Photoacoustic measurements of the thermal conductivity of some bulk polymer samples

Thermal parameters such as thermal diffusivity and thermal conductivity of the polymers nylon 66, cellulose acetate, polyacetal, Teflon, and polystyrene have been determined using the photoacoustic technique. Samples having thickness of the order of 25–50 μm have been specially prepared from bulk solid samples for measurements. The experimental method involves the determination of the characteristic frequency fc by measuring the variation of the amplitude and phase of the photoacoustic signal as a function of the chopping frequency for a monochromatic incident beam. Front surface illumination geometry has been used in the measurements. The measured thermal properties agree with the existing values in literature.

Thermal properties of La0.5Sr0.5Co1−xNixO3−δ ceramics using photopyroelectric technique

La0.5Sr0.5Co1−xNixO3−δ (0⩽x⩽0.6) ceramics were prepared using a conventional solid-state ceramic route. The thermal properties—thermal conductivity and heat capacity—of these ceramics were measured by the photopyroelectric technique. The thermal conductivity was found to increase with increasing Ni content. These materials were also found to exhibit a metallic-type variation of thermal conductivity with temperature, and no metal-insulator (M-I) transition was found to occur in any of the samples prepared by this route. However, a M-I transition was found to occur in La0.5Sr0.5CoO3−δ samples prepared by hot pressing. The difference is attributed to variations in oxygen content in the samples.

Carrier-type reversal in metal modified chalcogenide glasses: Results of thermal transport measurements

It is known that chalcogenide glasses, in general, are p-type semiconductors. This is attributed to the following two reasons. (i) The number of electrons excited above the conduction band mobility edge is smaller than the number of holes excited below the valence band mobility edge. (ii) The lifetime of the free holes excited from positive defect states is higher than the lifetime of free electrons excited from negative defect states. Moreover, chalcogenide glasses are rather insensitive to impurity doping because their Fermi levels are pinned near the middle of the band gap by valence alternation pairs. However, it is found that the chemical modification of certain chalcogenide glasses by metallic elements such as lead and bismuth changes the conduction to n type at specific metal concentrations. This phenomenon, called carrier-type reversal (CTR), is explained in terms of the unpinning of the Fermi level and the consequent enhancement in electron concentration in the medium. In this work we report the ...