David Schiferl

Calibration of the ruby R1 and R2 fluorescence shifts as a function of temperature from 0 to 600 K

Recent work by Gupta and Shen [Appl. Phys Lett. 58, 583 (1991)] has shown that in a nonhydrostatic environment, the frequency of the ruby R2 line provides a reliable measure of the mean stress or pressure. When using the frequency of either the R1 or R2 line to measure pressure at nonambient temperature, it is necessary to know the temperature dependence of the line shift. Unfortunately, the shift of the R2 line with temperature has not been reported. The ruby R1 and R2 fluorescence shifts have been determined as a function of temperature from 15 to 600 K. Both can be fitted very well to the simple cubic forms R1(T) =14 423+4.49×10−2T−4.81×10−4T2+3.71×10−7T3 cm−1 and R2(T)=14 452 +3.00×10−2T−3.88×10−4T2+2.55×10−7T3 cm−1. From 300 to 600 K the shifts fit well to linear functions of temperature. In addition, it is found that the R1‐R2 splitting changes by about 3 cm−1 over the 600 K temperature range. Linewidths were found to vary both with temperature and from sample to sample.

The diamond 13C/12C isotope Raman pressure sensor system for high-temperature/pressure diamond-anvil cells with reactive samples

By using a thin 13C diamond chip together with a 12C diamond chip as sensors, the diamond Raman spectra provide the means to measure pressure precisely (±0.3 GPa) at any temperature (10–1200 K) and simultaneous hydrostatic (or quasihydrostatic) pressure (0–25 GPa) for any sample compatible with an externally heated diamond-anvil cell. Minimum interference between the Raman spectrum from the diamond anvils and those of the pressure sensors is obtained by measuring pressures with the Raman signal from the 13C diamond chip up to 13 GPa, and that from the 12C chip above 10 GPa. The best crystallographic orientation of the diamond anvils is with the [100] direction along the direction of applied force, in order to further minimize the interference. At 298 K, the pressure dependence of the 13C diamond first-order Raman line is given by ν(P)=νRT+aP for 91 at. % 13C diamond, where νRT(13C)=1287.79±0.28 cm−1 and a(13C)=2.83±0.05 cm−1/GPa. Analysis of values from the literature shows that the pressure dependence of...

Comparison of the pressure‐induced frequency shift of Sm:YAG to the ruby and nitrogen vibron pressure scales from 6 to 820 K and 0 to 25 GPa and suggestions for use as a high‐temperature pressure calibrant

The pressure‐induced frequency shift of the Sm:YAG Y1 peak at elevated temperature is calibrated against the temperature‐corrected Raman shift of the nitrogen vibron and, at temperatures less than 673 K, the R1 shift of ruby. The results presented here indicate that pressure can be determined from the Y1 and Y2 peak frequencies, without temperature correction, from 6 to 820 K and from 1 bar to 25 GPa by using the equations: P(GPa) =−0.12204 (ωY1obs−16187.2) and P(GPa)=−0.15188 (ωY2obs−16232.2). However, pressure determinations based on Y2 are less accurate, especially at high temperature. At elevated temperature, the Sm:YAG Y1 and Y2 peak frequencies are most accurately determined by curve fitting a spectral window at least 400 cm−1 wide. The spectral range was chosen in order to include the decay of the intensity of the Lorentzian Y1 peak to a background value and incorporate a third peak at 16360 cm−1.

Raman spectroscopy and melting of nitrogen between 290 and 900 K and 2.3 and 18 GPa

Raman spectroscopy was used to study the melting of nitrogen from 290 to 900 K at pressures from 2.3 to 18 GPa. This work, which extends the melting by a factor of 9 over previously published results was made possible by new developments in high‐temperature diamond‐anvil cells. The β/δ phase boundary was also determined, and the β–δ–fluid triple point was found to be at 578±10 K and 9.9±0.5 GPa. The Raman frequencies of the vibron in fluid N2 and the ν2 vibron in δ‐N2 were found to have the same pressure dependence and be independent of temperature to a good approximation. A temperature‐independent pressure scale, useful to at least 900 K is approximated by P/GPa=0.4242 ν/cm−1 −987.8, where ν is the frequency of either the ν2 vibron in δ‐N2 or the vibron in fluid‐N2.

Pressure and temperature dependence of laser‐induced fluorescence of Sm:YAG to 100 kbar and 700 °C and an empirical model

The inability to measure pressure with accuracy at high temperature has been a hindrance to the development of simultaneous high‐temperature, high‐pressure experimental techniques. The results of recent laser‐induced fluorescence studies at high temperature and high pressure indicate that Sm:YAG is a promising pressure calibrant with very low‐temperature sensitivity. The most intense feature in the fluorescence spectrum is a doublet at 16186.5 cm−1. The Sm:YAG doublet exhibits a pressure‐induced peak shift comparable to the R1 shift of ruby. However, the temperature‐induced shift of the doublet is almost two orders of magnitude less than that observed for the R1 peak. Simultaneous high‐pressure‐temperature experiments indicate that the pressure and temperature effects on the frequency and line shape can be added linearly. An empirical model based on the linear combination of pressure dependent frequency shift and temperature dependent linewidth and intensity ratio successfully predicts the doublet line sh...

A high P-T single-crystal X-ray diffraction study of thermoelasticity of MgSiO3 orthoenstatite

P-V-T data of MgSiO3 orthoenstatite have been measured by single-crystal X-ray diffraction at simultaneous high pressures (in excess of 4.5 GPa) and temperatures (up to 1000 K). The new P-V-T data of the orthoenstatite, together with previous compression data and thermal expansion data, are described by a modified Birch-Murnaghan equation of state for diverse temperatures. The fitted thermoelastic parameters for MgSiO3 orthoenstatite are: thermal expansion ∂α/∂P with values of a=2.86(29)×10-5 K-1 and b=0.72(16)×10-8 K-2; isothermal bulk modulus KTo=102.8(2) GPa; pressure derivative of bulk modulus K′=∂K/∂P=10.2(1.2); and temperature derivative of bulk modulus K=∂K/∂T=-0.037(5) GPa/K. The derived thermal Grüneisen parameter is γth=1.05 for ambient conditions; Anderson-Grüneisen parameter is δTo=11.6, and the pressure derivative of thermal expansion is ∂α/∂P=-3.5×10-6K-1 GPa-1. From the P-V-T data and the thermoelastic equation of state, thermal expansions at two constant pressures of 1.5 GPa and 4.0 GPa are calculated. The resulting pressure dependence of thermal expansion is Δα/ΔP=-3.2(1)× 10-6 K-1 GPa-1. The significantly large values of K′, K, δTand ∂α/∂P indicate that compression/expansion of MgSiO3 orthoenstatite is very sensitive to changes of pressure and temperature.

Silicone fluid as a high‐pressure medium in diamond anvil cells

The usefulness of a silicone oil, Dow Corning 200, as a pressure medium in diamond anvil cells has been investigated. Common indicators of deviatoric stresses on ruby, such as changes in the R‐line widths and the R2‐R1 peak separation, show that this fluid does not deviate from hydrostaticity up to ∼15 GPa (150 kbar). The behavior of silicone is found to be very similar to the commonly used 4:1 methanol:ethanol mixture, while being much easier to use because of its higher viscosity. This ease of use and excellent performance makes silicone fluid a superior pressure medium.

Calibration of the nitrogen vibron pressure scale for use at high temperatures and pressures

Coherent anti‐Stokes Raman scattering (CARS) and spontaneous Raman spectroscopy have been used to obtain vibrational spectra of shock‐compressed and static high‐pressure fluid nitrogen, respectively. Vibrational frequencies were obtained from the CARS data using a semiclassical model for these spectra. Spontaneous Raman vibrational frequencies were determined by fitting data using a Lorentz‐shape line. A functional form was found for the dependence of the vibrational frequency on pressure and temperature to 40 GPa and 5000 K, respectively. By fitting the vibrational data to this form, a pressure scale based on the fluid nitrogen vibron has been calibrated for use at very high temperature. The nitrogen vibron pressure scale was used to determine the fluid‐δ nitrogen phase boundary up to 20 GPa and 900 K.

Temperature compensated high‐temperature/high‐pressure Merrill–Bassett diamond anvil cell

A Merrill–Bassett diamond anvil cell for high‐temperature/high‐pressure studies up to 5 GPa at 1000 K and 13 GPa at 725 K is described. To maintain uniform, well‐characterized temperatures, and to protect the diamond anvils from oxidation and graphitization, the entire cell is heated in a vacuum oven. The materials are chosen so that the pressure remains constant to within ±10% over the entire temperature range.

P- V- T Data of hexagonal boron nitride h BN and determination of pressure and temperature using thermoelastic equations of state of multiple phases

Abstract A synchrotron x-ray diffraction study on hexagonal boron-nitride (hBN) was conducted at simultaneous high pressures and temperatures. The pressure applied to the sample is pseudo-hydrostatic up to 9.0 GPa and the temperature was homogeneous in the range of 300 K to 1280 K. A modified Rietveld profile refinement has been applied to these diffraction spectra of low symmetry and multiple phases observed in the energy-dispersive mode. Thermoelastic parameters of hBN were derived by fitting a modified high temperature Birch-Murnaghan equation of state. The results are: bulk modulus K=17.6 GPa, pressure derivative K′=∂K/∂P=19.5, temperature derivative [kdot]=∂K/∂T=−0.69 × 10−2 Gpa/K, volumetric thermal expansivity α=a+bT with values of a=4.38 × 10−5K−1 and b=1.75 × 10−8K−2, respectively. It is observed that the thermal expansion and compression along different crystal axes are significantly different. The crystal c-axis is much more expandable and compressible than the a-axis. This is attributed to the...