Numerical calculations of the temperature distribution and the cooling speed in the laser-heated diamond anvil cell

Abstract

Numerical calculations have been done to reveal temperature distributions and cooling speeds of laser-heated samples in a diamond anvil cell. The distributions were calculated for variable experimental parameters including the diameter of the laser beam, anvil gap, and sample. The results show that the radial temperature distribution in all samples is Gaussian. The axial temperature gradient is ∼10 K/μm in samples heated by a broad laser beam of 100 μm diameter, and is ∼102 K/μm when a narrow laser beam of 10 μm diameter is used. The broad beam can generate a less extreme temperature gradient in both radial and axial directions as compared with the narrow beam, whereas the temperature gradient strongly depends on the anvil gap, although this is minimized when a narrow beam is used. When the narrow beam is used to heat samples, the surface temperature of the anvil culet can be kept below 400 K; thus, the narrow beam is suitable for heating samples under high pressure while keeping anvil temperatures low. Cooling speeds of the laser-heated samples were found to be from 100 to 102 K/μs. The discrepancy between actual sample temperature and measured temperature was also evaluated. To measure the peak temperature of a sample heated by a laser with a Gaussian power distribution within 5% accuracy, radiation from a circular area of less than (1/2)σ of the Gaussian must be observed.

Rhombohedral (9R) and hexagonal (6H) perovskites in barium silicates under high pressure

“…The Rietveld analysis was performed using GSAS (Larson and Von Dreele 2004) even though small, untransformed peaks (2θ = 7. 2°, 8.2°, 8.8°, 9.7°) were in the pattern because of the vertical temperature gradient in the laser heated DAC (Morishima and Yusa 1998). As shown in Figure 2, the 9R perovskite is a possible structure for the high-pressure phase.…”

α-Gd2S3-type structure inIn2O3Yusa1, Tsuchiya2, Tsuchiya3 et al. 2008Phys. Rev. B447352View full textAdd to dashboardCite

“…1͑d͔͒, one can realize that several broad diffraction lines appear around 8.0°, 8.2°, 9.0°, 11.5°, 12.8°, 14.0°, 16.0°, and 16.1°, which might be derived from a metastable phase being formed in the colder part at the contact surface with diamond anvils. 21 Since the broad peaks often appear in the same kind of experiments, 9,22 we eliminated them from the input data to search for the unit cell. Then, we successfully determined an orthorhombic unit cell with a = 5.473͑1͒ Å, b = 3.003͑1͒ Å, and c = 11.618͑3͒ Å by using 31 peaks.…”

Temperature gradients in the laser‐heated diamond anvil cell

“…However, axial gradients still exist, and the influence of these gradients on the average temperature of a diffraction volume, however, can greatly affect the inferred values for thermal expansion and thermal pressure [Kavner, 2001]. The effect of insulation layers on the heat flow is addressed by numerical calculations [Dewaele et al, 1998;Morishima and Yusa, 1998] and scaling analysis [Panero and Jeanloz, 2001]. Thus we consider the simpler problem of no insulation layers because it is (1) experimentally testable, (2) involves fewer model parameters, and (3) corresponds to the actual conditions of many experiments.…”

“…Ehsting numerical models have treated this problem for the case of the TEMoo mode only [Bodea and Jeanloz, 1989; Dewaele et al, 1998; Morishima and Yusa, 1998] and neglect the temperature dependence of thermal conductivity. We find that an analytic technique can describe the temperature distribution in the diamond cell and help constrain the thermal conductivity of samples at high pressures and temperatures.…”