AN ABSTRACT OF THE THESIS OF ROBERT EDWARD HOLMES for the Ph. D. in Chemistry (Name) (Degree) (Major) Date thesis is presented September 3, 1965 Title ELECTRICAL AND OPTICAL PROPERTIES OF POTASSIUM CHLORIDE SINGLE CRYSTALS CONTAINING LEAD ION Abstract approved Redacted for Privacy (Major professor) 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 meth- od of purification produced a salt with < O. 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 at- mosphere 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 scan- ning 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 O. 11. A preliminary investigation of the thermal sensitivity of the A band and some other bands due to lead ion, ob- served 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 un- der 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 appar- ent 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 O. 1 eV or greater. An anomaly in the experimental conductivity curves is explained by the loss of lead ion from crystals. ELECTRICAL AND OPTICAL PROPERTIES OF POTASSIUM CHLORIDE SINGLE CRYSTALS CONTAINING LEAD ION by ROBERT EDWARD HOLMES A THESIS submitted to OREGON STATE UNIVERSITY in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY June 1966 APPROVED: Redacted for Privacy Professor of Chemistry In Charge of Major Redacted for Privacy !. Chairman of Department of Chemistry Redacted for Privacy Dean of Graduate School Date thesis is presented September 3, 1965 Typed by Opal Grossnicklaus DEDICATION To my wife Marilyn, whose untiring support, encouragement, and understanding made this possible. ACKNOWLEDGMENTS The author is indebted to Dr. Allen B. Scott for numerous suggestions, valuable criticisms and discussions, and to the Office of Naval Research for material support. Dr. Donald Conant was a collaborator in the design of some sections of the controlled- atmosphere crystal -growing apparatus. His assistance is gratefully acknowledged. The use of the ion exchange columns for KC1 purification, furnished by Dr. W. J. Fredericks, and the conductivity cell furn- ished by Dr. Allen B. Scott is sincerely appreciated. To my friends who helped with the proof reading of the manu- script, D. Hinks, L. Lewis, B. Newton, and L. Scheurman, many thanks. Especial thanks to C. D. Woods whose assistance in convert- ing theoretical design to functional practicality was invaluable. TABLE OF CONTENTS I GENERAL INTRODUCTION 1 II SALT PURIFICATION 5 Introduction 5 Purification by Fractional Recrystallization 7 Experimental 7 Purification by Ion Exchange 9 Experimental 10 Salt Purity: A Comparison 11 III PREPARATION OF SINGLE CRYSTALS 16 Introduction 16 Crystal - Pulling Apparatus 18 Rotating Cold Finger 18 Melt Furace 20 Furnace -Lowering Mechanism 20 Controlled- Atmosphere Crystal- Growing Apparatus 21 Cold Finger Assembly 21 Melt Furnace 25 Crystal Growth Chamber and Lid 27 Lowering Mechanism 28 Vacuum and Controlled- Atmosphere System 28 Single - Crystal Growth 30 Experimental 30 Contamination from Atmosphere and Crucible 33 Uniformity of Doping 36 Results 38 IV OSCILLATOR STRENGTH 40 Introduction 40 Trace Analysis of Lead in KC1 with Dithizone 43 Reagent Purification 47 Ammonia - Cyanide -Sulfite Solution 49 pH Control 50 Glassware 50 Experimental 50 Discussion of Results 52 Homogeneity 57 Scanning Absorption Cell 57 Experimental 62 TABLE OF CONTENTS (Continued) Incorporation of Lead Ion in KC1 Crystals 64 Band Shape Analysis 73 Oscillator Strength Evaluation: Summary and Discussion of Results 78 V TRANSPORT OF LEAD ION IN KCL 85 Introduction 85 Theory 87 Electrolytic Transport 93 Plane Source 94 Extended Initial Distribution 100 Transport Apparatus 101 Experimental 110 Experimental Particulars, Results and Discussion 116 Absorption by an Inhomogeneous Medium 117 Diffusion and Transport from a Plane Source 122 Diffusion and Electrolytic Transport from an Extended Source 127 Comparison with Results of Fredericks and Scott 142 Migration of Pb ++ in KC1:Pb, Ca 150 Mobility and Effective Charge of Pb ++ in KC1 151 VI IONIC CONDUCTIVITY 155 Introduction 155 Theory 157 Apparatus 160 Experimental 161 Results and Discussion 164 Pure KC1 Crystals 164 Lead Doped Crystals 168 VII SUGGESTIONS FOR FURTHER WORK 180 BIBLIOGRAPHY 182 LIST OF FIGURES Figure 3. 1 Crystal pulling apparatus. 19 3. 2 Photograph of the controlled -atmosphere crystal -growing apparatus. 22 3. 3 Schematic diagram of the controlled- atmosphere crystal - growing apparatus. 23 3. 4 Schematic diagram of the atmosphere control system for the crystal- growing apparatus 29 4. 1 Absorption curves of Dithizone, its oxidation product, and Pb- dithizonate, all in CC14. 46 4. 2 Determination of lead in KCl single crystals with dithizone in CC14. 53 4. 3 Scanning absorption cell and cover. 58 4. 4 Reference backing plate and sample mount; sample backing plate and mount; various slits. 60 4. 5 Typical homogeneity data (Scanning absorption cell). 63 4. 6 Corrected homogeneity data. Point analysis of the con- tinuous curve, fig. 4. 5. 65 4. 7 Thermal sensitivity of air -grown KC1:Pb crystals. 67 4. 8 Absorption spectra of KC1 and KC1:Pb showing the presence of side bands in the 250 -273 mµ region. 70 4. 9 Shape of the A -band in KC1:Pb. 74 4. 10 Graph of log (Relative absorbance) versus (E -EA)2. 76 4. 11 Comparison of the A -band shape against a double Gaussian shape. 77 5. 1 Concentration -distance curves for diffusion and electroly- tic transport from a plane source. 96 5. 2 Concentration -distance curves for diffusion and electroly- tic transport from an extended initial distribution. 102 5. 3 Photograph of the crystal transport apparatus. 103 5. 4 Transport cell and envelope. 106 5. 5 Schematic diagram of the transport cell clamp, electrode assembly, and crystal stack. 108 5. 6 Schematic diagram of the controlled- atmosphere system for the transport cell. 109 5. 7 Typical transport profile determined in the scanning absorption cell. 113 5. 8 Comparison of the absorption curve (A =0. 87) predicted by Jones's theory with an experimental curve. 119 5. 9 Diffusion and electrolytic transport profile of D -1 and T -1 124 5. 10 Diffusion and electrolytic transport profile of D -2 and T -2. 125 LIST OF FIGURES (Continued) Figure 5. 11 Concentration profile of the vapor phase diffusion of PbC12 into KC1; crystal D -20. 128 5. 12 Diffusion profile of crystal sample D -3. 132 5. 13 Electrolytic transport profile of crystal T -3. 133 5. 14 Electrolytic transport profile of crystal T -7. 134 5. 15 Electrolytic transport profile of crystal T -10. 135 5. 16 Electrolytic transport profiles of crystal T-11. 136 5. 17 Electrolytic transport profiles of crystal T -11. 137 5. 18 Electrolytic transport profile of crystal T -12, section a. 138 5. 19 Electrolytic transport profile of crystal T -12, section b. 139 5. 20 Electrolytic transport profile of crystal T -12, section c. 140 5. 21 Typical electrolytic transport profile after Fredericks and Scott. 143 5. 22 Electrolytic transport profile of crystal F -T -6. 146 5. 23 Electrolytic transport profile of crystal T -15. 148 5. 24 Electrolytic transport profile of crystal T -16. 149 6. 1 Typical conductivity curve of an ionic crystal containing impurities. 150 6. 2 Conductivity cell and electrical circuit. 162 6. 3 Specific conductivity of KC1 crystals. 166 6. 4 Specific conductivity of KC1:Pb crystal 10. 170 6. 5 Specific conductivity of KC1:Pb crystal 9. 171 6. 6 Specific conductivity of KC1:Pb crystal 12. 172 6. 7 Specific conductivity of KC1 crystals.