Synthetic diamonds produce pressure of 125 GPa (1.25 Mbar)
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I. INTRODUCTION Diamonds have intrigued mankind for millenia.1'2 Their properties have been extensively studied,3 5 and the way they form in nature is a matter of great interest. The history of the synthetic production of diamonds is also very exciting.5"9 The first synthetic diamonds produced by the General Electric Company were made in experiments on 15 and 16 December 1954. Two of the most important patents were obtained by scientists at the General Electric Company in 1960.10 A large industry for the production of synthetic industrial diamonds now exists.5 The first announcement of the production of sizeable gem quality diamonds was made by the General Electric Company on 28 May 1970. n The basis of the thermodynamics and kinetics of the process used at the General Electric Company for the growth of the gems is published in three papers12"14 and in patents.15 The General Electric Company process is described in Refs. 7 and 8 and in a paper by Strong.16 The chemical, physical, and optical properties of these synthetic diamonds have also been characterized in considerable detail by others.17"19 Diamonds are the ideal material for creating pressures in the megabar regime (1 Mbar = 100 GPa). They have extremely high yield strengths and hardness as well as extreme rigidity.4 Because of their enormous strengths they can be used to generate enormous pressures. It has been predicted that perfect crystals of diamonds should be capable of supporting pressures of 7 Mbar (700 GPa), 20 and there is experimental evidence that pressures in excess of 4 and 5 Mbars have been created using natural diamonds.21'22 The pressure was measured by placing a ruby on top of the sample and measuring the shift of the ruby fluorescence and using a function P(A) that had been calibrated earlier at lower pressures against the equations of state of different materials determined by shock data.23 Diamonds are transparent to optical radiation with wavelengths from 230 to 2500 nm depending on the type of diamonds.3'4 They are therefore good optical win614
J. Mater. Res. 2 (5), Sep/Oct 1987
http://journals.cambridge.org
dows for making spectroscopic studies. In addition, diamonds have a low atomic number and hence are relatively transparent to high-energy x-ray radiation. They are therefore ideal materials as x-ray windows for studying x-ray diffraction of samples in the megabar regime. The use of natural diamonds for generating very high pressures and for studying different materials at these pressures is described in detail by Jayaraman.24'25 They are used in devices known as diamond anvil cells (DAC). A schematic of the diamonds and gasket used in the DAC is shown in Fig. 1. Thus far all scientific studies of samples in a sample hole in a gasket have used natural diamonds. Recently Onodera etal. used a pair of deep yellow synthetic diamonds of type IB with a flat tip to generate a pressure of 68 GPa (as measured by the ruby shift) in a gasket without a sample hole.26 The pressure was measured by the shift of the fluorescence of a ruby that h
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