MECHANICAL AND OPTICAL RESPONSE OF DIAMOND CRYSTALS SHOCK COMPRESSED ALONG DIFFERENT ORIENTATIONS By JOHN MICHAEL LANG, JR. A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY WASHINGTON STATE UNIVERSITY Department of Physics DECEMBER 2013 © Copyright by JOHN MICHAEL LANG, JR., 2013 All Rights Reserved © Copyright by JOHN MICHAEL LANG, JR., 2013 All Rights Reserved To the Faculty of Washington State University: The members of the Committee appointed to examine the dissertation of JOHN MICHAEL LANG, JR. find it satisfactory and recommend that it be accepted. ___________________________________ Yogendra M. Gupta, Ph.D., Chair ___________________________________ Matthew D. McCluskey, Ph.D. ___________________________________ Philip L. Marston, Ph.D. ii ACKNOWLEDGMENTS I would first like to thank my advisor, Dr. Yogendra Gupta, for providing me with this research opportunity and supporting my work. His guidance and leadership was invaluable to my education and training as a scientist. I am very grateful for his time and effort. I would also like to thank Dr. Matt McCluskey and Dr. Philip Marston for their advice and guidance, and for serving on my committee. I would like to thank the administrative and technical staff of the Institute for Shock Physics for their support of my work. Special thanks to Kurt Zimmerman and Yoshi Toyoda for their assistance with the experimental instrumentation, to Nate Arganbright for his help with materials preparation, to Steve Barner for machining many of the parts used in this work, and to Kent Perkins, Cory Bakeman, and Luke Jones for operating the guns. A warm thank you to Sabreen Dodson and the administrative staff of the Physics Department for their help in guiding me through the policies and requirements of the Graduate School. I would also like to thank JiaJia Chang for her patience and support. Lastly, I would like to thank my parents, John and Anne Lang, my sister, Elizabeth, and my grandparents for their love, generosity, and encouragement as I worked to complete my degree. It was their support that enabled me to finish, and I dedicate my dissertation to them. This work was supported by the DOE/NNSA. iii MECHANICAL AND OPTICAL RESPONSE OF DIAMOND CRYSTALS SHOCK COMPRESSED ALONG DIFFERENT ORIENTATIONS Abstract by John Michael Lang, Jr., Ph.D. Washington State University December 2013 Chair: Yogendra M. Gupta To determine the mechanical and optical response of diamond crystals at high stresses and to evaluate anisotropy effects, single crystals (Type IIa) were shock compressed along the [100], [110], and [111] orientations to ~120 GPa peak elastic stresses. Particle velocity histories and shock velocities, measured using laser interferometry, were used to examine nonlinear elasticity, refractive indices, and Hugoniot elastic limits of shocked diamond. Time-resolved Raman spectroscopy was used to measure the shock compression induced frequency shifts of the triply degenerate 1332.5 cm-1 Raman line. Longitudinal stress-density states for elastic compression along different orientations were determined from the measured particle velocity histories and elastic shock wave velocities. The complete set of third-order elastic constants was determined from the stress-density states and published acoustic data. Several of these constants differed significantly from those calculated using theoretical models. The refractive index of diamond shocked along [100] and [111] was determined iv from changes in the optical path length along the direction of uniaxial strain. Linear photoelasticity theory predicted the measured refractive index along [111]. In contrast, the refractive index along [100] was nonlinear. The refractive indices for [110] compression were not determined, but the data showed evidence of birefringence. The splitting and frequency shifts of the diamond Raman line were measured for shock compression along [111] and were in good agreement with predictions from prior shock work. Frequency shifts were also measured along [100] and [110] up to ~60 GPa, extending previous measurements. The anharmonic force constants determined from all shock compression measurements agree with the previous shock compression determinations. Hugoniot elastic limits for diamond shock compressed along different orientations were determined from the measured wave profiles. The elastic limits for the three orientations were highest at ~90 GPa peak elastic stress, but decreased at the higher peak elastic stress. Shear strengths were determined from the measured elastic limits: shocked diamond was strongest for compression along [110] and weakest for compression along [111]. The shear strength dependence on shock propagation direction was correlated with the stress magnitude normal to the slip plane, which appeared to inhibit the onset of inelastic deformation. v TABLE OF CONTENTS Page ACKNOWLEDGMENTS..................................................................................................iii ABSTRACT.......................................................................................................................iv TABLE OF CONTENTS....................................................................................................vi LIST OF TABLES..............................................................................................................xi LIST OF FIGURES..........................................................................................................xiii CHAPTER 1. INTRODUCTION...................................................................................................1 1.1 Objectives and Approach.............................................................................3 1.2 Organization of Chapters.............................................................................4 References for Chapter 1.........................................................................................6 2. BACKGROUND.....................................................................................................9 2.1 Crystal Properties.........................................................................................9 2.2 Elastic Response of Diamond....................................................................11 2.2.1 Linear Elastic Response.................................................................11 2.2.2 Nonlinear Elasticity: Finite Strain Theory.....................................13 2.2.3 Third-order Elastic Constants of Diamond....................................15 2.2.4 Application to Uniaxial Strain.......................................................17 2.3 Refractive Index of Shocked Diamond......................................................21 2.3.1 The Optical Indicatrix....................................................................21 2.3.2 Photoelasticity Theory...................................................................24 vi 2.3.3 Application to Diamond.................................................................25 2.4 Raman Spectrum of Shocked Diamond.....................................................27 2.4.1 Strain-induced Frequency Shifts....................................................28 2.4.2 Past Experimental Work.................................................................29 2.5 Elastic Limit and Strength of Shocked Diamond......................................30 2.5.1 Theoretical Background.................................................................31 2.5.2 Past Studies on Diamond Strength.................................................33 References for Chapter 2.......................................................................................38 3. EXPERIMENTAL METHODS.............................................................................43 3.1 Materials Characterization.........................................................................43 3.1.1 Diamond.........................................................................................43 3.1.2 OHFC Copper................................................................................44 3.1.3 Tantalum........................................................................................45 3.1.4 Lithium Fluoride............................................................................45 3.2 Mechanical Response and Refractive Index Measurements......................46 3.2.1 Experimental Configuration...........................................................46 3.2.2 Target Construction........................................................................48 3.2.3 Projectile Construction...................................................................52 3.2.4 Instrumentation..............................................................................52 3.3 Raman Spectroscopy Measurements.........................................................56 3.3.1 Experimental Configuration...........................................................56 3.3.2 Target Construction........................................................................58 3.3.3 Projectile Construction...................................................................62 vii 3.3.4 Instrumentation..............................................................................62 3.3.5 Triggering and Synchronization.....................................................66 3.3.6 Spectral and Temporal Calibration................................................70 References for Chapter 3.......................................................................................73