Synthesis and characterization of 6-alkylcarbamato-2, 10-dichlorodibenzo [d,g] [1,3,6,2]dioxathiaphosphocin 6-oxides

Novel 6-alkylcarbamato/thiocarbamato-2,10-dichlorodibenzo [d,g][1,3,6,2]dioxathiaphosphocin 6-oxides were synthesized by cyclization of 5,5′-dichloro-2,2′-dihydroxydiphenyl sulfide with the corresponding dichlorophosphinyl carbamates/thiocarbamates that were obtained by the addition of alcohols/thiols to dichloroisocyanatophosphine oxide and were characterized by IR, ¹H, ¹³C, ³¹P NMR, and mass spectral studies. A ¹³C NMR analysis revealed ²J_POC and ³J_POCC couplings. © 1996 John Wiley & Sons, Inc.     

Effect of Electric Field on Dielectric Properties of SnO2 Sb2O3 and their Mixed Thin Films

Thin films of various thicknesses in the MIM structure have been prepared from the the powders of SnO₂, Sb₂O₃ and (SnO₂ + Sb₂O₃) of high purity by the thermal evaporation technique in a vacuum of 10⁻⁵ Torr. Dielectric properties of SnO₂, Sb₂O₃, and their mixed thin films have been studied with ac and dc electric fields and frequency. Capacitance and loss tangent are almost independent on dc voltage upto 1.0 V for SnO₂, 10.0 V for Sb₂O₃ and 2.5 V for mixed films. These capacitors become unstable at 1.0 V for SnO₂ films and 2.5 V for mixed films. For higher film thicknesses the decay in these films starts at higher voltages. Capacitance and loss tangent increases with applied ac voltage in SnO₂, Sb₂O₃, and their mixed films. A comparison of the capacitance values of SnO₂, Sb₂O₃, and their mixed films showed that the capacitance values are less in Sb₂O₃ as compared to SnO₂ films. In mixed films the capacitance is greater than the constituent films. These studies have shown that Sb₂O₃ films are found to be more stable compared to SnO₂ and their mixed films for ac and dc voltages. The results thus obtained on SnO₂, Sb₂O₃, and their films are presented and discussed.     

Role of Impurity Precipitates on Microhardness of KBr:Ba2+ Crystals

Microhardness of KBr crystals doped with various concentration of Ba²⁺ have been investigated in the asgrown state and after quenching from various elevated temperatures. It is observed that hardness increases with increase in impurity concentration and at high concentration the hardness starts decreasing. Microstructural investigations have showed the formation of visible precipitates at high concentrations. The heat treatment studies showed that in crystals quenched from elevated temperatures the visible precipitates dissociate and hardness increases.     

Thermoluminescence studies of Al2O3 crystals doped with Cobalt impurity

Thermoluminescence (TL) studies of cobalt-doped Al₂O₃ crystals irradiated with X-rays have shown that the TL glow curve consists of three peaks at 105, 195 and 260°C. Bleaching, annealing and quanching studies have been performed in order to understand the nature of colour centers responsible for the formation of the three peaks. The values of the fundamental parameters like trap depth and frequency factor are estimated from TL data and the results obtained are discussed.     

High-temperature X-ray irradiation induced thermoluminescence and half-life calculations in NaYF4 polycrystalline samples

Elevated irradiation temperature studies with NaYF₄ samples reveal that the intensity of the two glow peaks observed around 120 and 180°C enhances. The effect of temperature of irradiation (T_irr) on the sensitisation of the both peaks are studied. The half lives of these glow peaks were calculated and concluded that the half lives of these peaks decreases with the increase in irradiation temperatures.     

Cosmic Strings and Domain Walls in a Scale-Covariant Theory of Gravitation

Axially symmetric space-time is considered in the presence of cosmic string source and thick domain walls in the frame work of a scale-covariant theory of gravitation. A relation between metric potential is assumed to get a determinate solution of the field equations of this theory. In this particular case, it is observed that the geometric (Nambu) string p-string (Takabayasi string) and Reddy string do not survive. It is also seen that the stiff (self-gravitating) domain walls do not exist in this theory.