THE AMT]RICAN MINDRALOGIST, VOL. 54, NOVEMBER-DECEMBER, 1969 SLIP SYSTEMS IN QUARTZ: I. EXPERIMENTS R. D. Bejiral aNp K. H. G. Asnnoe , H. H. Wills Physics Laboratory, []niversity of Bristol,, England. ABsrRAcr Single crystals of synthetic quartz were cut into compression test specimens of various orientations and deformed at elevated temperatures and at atmospheric pressure. No macroscopic evidence of plastic flow was detected at an imposed strain rate of 10-3 sec.-r' At an imposed strain rate of 10-a sec-l, plastic flow was possible only at temperatures above 600oC and, with a strain rate of 10-5 sec-l, there was plastic flow at 575'C and above. Below 700oC slip, was predominantly basal and in a crystallographic c direction. Between 700oC and 850oC, slip occurred with equal facility in the crystallographic a and c directions, and on many low index planes co-zonal with these directions. At 750oC and above, slip also occurred on pyramidal planes and in the directions (c*c). These observations are dis- cussed in terms of the nature of dislocation cores in quartz. INrnorucrroN In an earlier paper (Badta and Ashbee, 1967),evidence was reported for the plastic deformation at atmospheric pressureof synthetic crystals of quartz at temperatures close to or within the high-quartz field' The present work concerns a systematic investigation of this deformation in order to identify all the slip systems which can be operated at atmos- pheric pressure. Since the elastic strain energy of a dislocation is pro- portional to the modulus of its Burgers vector squared (Frank and Nicolas 1953), dislocations with small Burgers vectors are favoured. Thus, f or high-quartz, the most likely Burgers vectors are a <II20> and c [0001], of lengths 5.02 A and 5.48 A respectively. In the presentinvestigations, single crystal specimens were compressed in each of six orientations in order to subject different low index planes containing the vectors a, c or <s+c> to the highest resolved shearstress.The observed slip systems are reported, and structural considerations which would in- fluence the choice of slip vectors are discussed. In part II of this work, Iinear anisotropic elasticity theory is used to estimate the non-core energies of dislocations in quartz, and the "ease of slip" for several dislocations is considered. In particular, the criterion for basal and/or prismatic slip is discussed. Details of the stress-stain behaviour in the compressedspecimens,and the effects of crystal phase changeson the mode of deformation, are to be published elsewhere. ExpnnnmNtal Compression test specimens lvere cut in -the form of rectangular parallelopipeds from synthetic quartz crystals grown by the General Electric Company, Wembley. The dimen- 1 Present address: Department of Physics, University of Ghana, Legon, Ghana' t5s I
SLIP SYSTEMS IN QUARTZ: I. EXPERIMENTS
Jun 23, 2023
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