The Use of Quartz as an Internal Pressure Standard in High-Pressure Crystallography

Abstract

The unit-cell parameters of quartz, SiO2, have been determined by single-crystal diffraction at 22 pressures to a maximum pressure of 8.9 GPa (at room temperature) with an average precision of 1 part in 9000. Pressure was determined by the measurement of the unit-cell volume of CaF2 fluorite included in the diamond-anvil pressure cell. The variation of quartz unit-cell parameters with pressure is described by: a-4.91300 (11) = -0.0468 (2) P + 0.00256 (7) P~--0.000094 (6) p3, c -5.40482 (17) = -0.03851 (2) P + 0.00305 (7) p2 _ 0.000121 (6)/>3, where P is in GPa and the cell parameters are in ~ngstroms. The volume-pressure data of quartz are described by a Birch-Murnaghan thirdorder equation of state with parameters V0= 112.981 (2) ~3, KT0 = 37.12 (9) GPa and K' = 5.99 (4). Refinement of K" in a fourth-order equation of state yielded a value not significantly different from the value implied by the third-order equation. The use of oriented quartz single crystals is proposed as an improved internal pressure standard for high-pressure single-crystal diffraction experiments in diamond-anvil cells. A measurement precision of 1 part in 10 000 in the volume of quartz leads to a precision in pressure measurement of 0.009 GPa at 9 GPa.

High-pressure synthesis of a polyethylene/zeolite nano-composite material

“…Pressure-volume data for PESIL can be fitted to a third order Birch-Murnagam EOS 34 with a B 0 value of 26.7(2.0) GPa and the first derivative (B 0 ') of 4 ( Table 1). The encapsulated PE in PESIL thus remarkably increases the bulk modulus to a value, which is closer to that of a-quartz 35 , as in the case of CO 2 -and Ar-filled silicalite 26 . In addition, the density of PESIL is 2.054 (1) g cm À 3 , which is lower than that of a-quartz by about 22%, mainly because it is a SiO 2 /C n H 2n composite material.…”

Fluorinert as a pressure-transmitting medium for high-pressure diffraction studies

“…The physical parameters of the diffractometer at Virginia Tech are very similar to that in Bayreuth. 28 Of particular importance is that the instrument configurations lead to a full width at half maximum ͑FWHM͒ of the individual components of the ␣ 1 -␣ 2 doublet of the diffracted beams from the quartz sample of approximately 0.05°under hydrostatic conditions. This means that broadening of the peaks due to strain or any other cause is readily detectable.…”

Preferred orientation in experimentally deformed stishovite: implications for deformation mechanisms

“…2). In both experiments the DACs were closed and the samples were already at pressure for the first diffraction measurements; thus, we used ambient pressure volume 112.981 Å 3 for quartz (Angel et al 1997) and 46.55 Å 3 for stishovite (Wang et al 2012) when determining pressures. The isotropic size strain model was used to fit the peak widths by refining the parameters crystallite size and r.m.s.…”

“…The hydrostatic pressure was determined as a function of volume change with a Birch Murnaghan equation of state for quartz (Angel et al 1997) and for stishovite (Wang et al 2012). Volume was calculated from the cell parameters, which are determined by the hydrostatic peak position (taken at η = 54.7° from the compression direction, described in Singh et al 1998) along 2θ (Fig.…”