Graduate Thesis Or Dissertation
 

Electrical and optical properties of potassium chloride single crystals containing lead ion

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  • A survey of the methods of purification of KC1, for use in preparing single crystals by growth from the melt, was made. Two methods, fractional recrystallization and ion exchange, were used. The purity of the salt and crystals grown from the same salt were compared with the findings of other authors. The ion exchange method of purification produced a salt with < 0.01 ppm lead ion and the material was suitable as a "pure" host matrix for the study of the properties of lead ion in KC1 single crystals. Two crystal-growing apparatus were designed and built to produce pure and lead ion-containing KC1 single crystals in an atmosphere of air or other gases. A novel method of producing a "dual" crystal, one section pure, the other containing lead ion, in a continuous host crystal, was introduced. The incorporation of lead ion into these crystals was studied by means of spectrophotometry and evidence for the incorporation of the ion at more than one site was noted. The homogeneity of doping was considered a function of the crystal growth method and the manner of incorporation of the lead ion into the crystal. A scanning absorption cell was designed and built to observe the uniformity of lead ion distribution in the crystal. The dithizone method of trace analysis of lead was adapted to the analysis of KC1 single crystals containing lead. The oscillator strength of the 273 mμ band, called the A band, of lead ion in KC1 was found to be 0.11. A preliminary investigation of the thermal sensitivity of the A band and some other bands due to lead ion, observed in the 250-270 mμ region, was made. It was found that quenching from 600°C maximized the A band. The diffusion and electrolytic transport of lead ion were studied to evaluate the effective charge on the lead ion species migrating under the influence of an electric field. Migration was studied from both plane and extended sources and the mobility of the species at 560°C was found to be no greater than 8 x 10⁻⁹ cm²/volt sec. The effective charge on the species was determined to be no greater than 0.6 of an electronic charge. This value is smaller than the charge on the free lead ion, and it is suggested that the lead ion migrates as a complex. The possible complexes involve the association of positive ion vacancies or chloride ions with the lead ion. The reduction of lead ion to elemental lead near the junction between the pure and lead-containing regions partially explained the apparent migration of lead ion, in a field, toward the anode as observed by other authors. The conductivity of pure and lead ion-containing crystals was observed. The association energy of a positive ion vacancy with the lead ion was found to be about 0.1 eV or greater. An anomaly in the experimental conductivity curves is explained by the loss of lead ion from crystals.
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file details HolmesRobertE1966_Redacted.pdf 2017-08-04 Pubblico Scaricare