K. Goswami

Characterisation of semiconducting V2O5-Bi2O3-TeO2 glasses through ultrasonic measurements

Tellurite containing vanadate (50−x)V2O5–xBi2O3–50TeO2 glasses with different bismuth (x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi2O3 content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi2O3 content. The observed results confirm that the addition of Bi2O3 modifier changes the rigid formula character of TeO2 to a matrix of regular TeO3 and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO4 trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi2O3 content are more stable than with high Bi2O3 content.

Amorphous to crystalline transition of selenium thin films of different thicknesses

Abstract Thin films of amorphous selenium obtained by vacuum evaporation display an increase of “optical gap” E g opt with an increase of thickness of the film. From the observed dependence of E g opt on the thickness of the film, the influence of the thickness on the gap states is interpreted in terms of the density of states model proposed by Mott and Davis. The amorphous to crystalline transition obtained by heat treatment of the specimen is also investigated. The minimum temperature for an appreciable change in crystallisation determined by the transmission of light through selenium films is also a function of the thickness and binding energy of the films. The crystalline structures resulting from heat treatment at different temperatures have been identified by scanning electron microscopy. The generation of different crystalline structures is reported in terms of the thickness and preparation conditions of the amorphous films.

Range-energy relation of electrons in a KCl crystal

Abstract The range of electron in KCl 〈100〉 and KCl 〈110〉 crystals in the energy between 30 and 60 keV have been experimentally determined. The data fit an equation of the type, R = kE n . The values of k and n exhibit crystalline orientation dependence.

Mobility of F centers in electrolytically colored potassium halides

Abstract Single crystals of KCl and KI have been colored by the process of electron injection at various temperatures and applied voltages. F center mobility during bleaching was determined. The activation energy associated with the F center migration was estimated.

ON THE PRODUCTION OF F-CENTRES BY FAST ELECTRONS.

SummaryA single crystal of NaCl was bombarded with 25 keV electrons along (100) axis, and the corresponding depth of coloration due toF-centres was estimated. The number ofF-centres produced was compared with the number of incident electrons, and the rate ofF-centre production was found to be 52 per cent.RiassuntoSi è bombardato lungo l’asse (100) un singolo cristallo di NaCl con elettroni di 25 keV, e si è valutata la corrispondente profondità di colorazione dovuta ai centriF. Si è confrontato col numero di elettroni incidenti, il numero di centriF prodotti e si è trovato un valore del 52 per cento per la percentuale di produzione di centriF.РеэюмеМонокристалл NаСl бомбардировался злектронами с знергией 25 кзВ вдоль оси (100), и оценивалась соответствуюшая глубина окращивания, обусловленногоF центрами. Число рожденныхF центров сравнивалось с числом падаюших злектронов, и получено, что интенсивность рожденияF центров составляет 52%.

Dechanneling of electrons by thermally produced lattice vacancies in the crystals of alkali halides

Abstract Single crystals of NaCl, KCl and KI were heat treated at various elevated temperatures. Lattice vacancies generated in the crystals are found to dechannel the incident energetic electrons. A factor for the increase of the energy loss of electrons due to dechanneling is determined, which is observed to be an increasing function of the concentration of lattice vacancies.

Anomaly in electron channeling due to imperfections produced thermally in a potassium chloride crystal

Abstract Lattice imperfections were produced in KCl crystals by a thermal process. The heat treated specimen was irradiated with 50 KeV electrons and the corresponding range of electrons in the crystal has been estimated. It was found that the electron range in the crystal depends upon the temperature of heat treatment, being a decreasing function of this temperature up to about 625 K, above which it becomes an increasing function. This anomaly has been explained in terms of dissolution of vacancies through dislocation loops.