Laser heating, DACs

Since part of the interpretations for the intermediate Fe in perovskite and postperovskite is based on the XES analyses for the total spin momentum of the 3d electronics in the samples, further understanding of the XES spectra involving multiple electronic transitions as well as theoretical calculations incorporating lattice distortion effects is needed to resolve the discrepancy between current experimental and theoretical results and interpretations. Although SMS spectra can now be collected from the laser-heated DAC experiments at relevant P-T conditions of the lower mantle, extended time windows are needed to extract more meaningful information to decipher the spin and valence states of iron in the lower-mantle minerals at relevant P-T conditions. Knowing the exact spin and valence states of iron in the lower-mantle minerals would then help geophysicists to address properties of the deep Earth. 

Yoo C S, Akella J and Nicol M 1996 Chemistry at high pressures and temperatures in-situ synthesis and characterization of p-SijN by DAC x-ray/laser-heating studies Advanced Materials 96 ed M Akaishi et al (Tsukuba National Institute for Research in Inorganic Materials) p 175... 

Figure 11. Schematic representation of a laser heating experiment in the DAC. The IR laser beam is directed onto the absorbing sample immersed in a compression medium acting also as thermal insulator. The thermal emission of the sample is employed for the temperature measurement, while the local pressure is obtained by the ruby fluorescence technique (see next section).

Very recently, Solozhenko [540] reported the high-pressure-high-temperature synthesis of cubic BC2N with in situ control of the reaction by x-ray diffraction measurement. The first high-density product has been obtained in a laser-heated diamond anvil cell (DAC). The starting material was g-BC N, prepared... 

The technique of laser heating in a DAC is based on three main features optical transparency of diamond anvils the samples can be heated via the optical absorption of intense laser radiation, and the temperature can be determined from the thermal radiation spectrum of the heated sample using the Planck formula [10]. Laser radiation for heating of a sample in a DAC was first implemented by Ming and Bassett [11], who used a pulsed ruby laser, and a continuous-wave Nd-YAG (yttrium-aluminum-garnet) laser to heat samples in a DAC above 3300 K, and up to 2300 K, respectively. Today two types of continuous wave infrared (IR) lasers are extensively used in laser heating experiments Solid state lasers (Nd-doped YAG, or YLF (yttrium-lithium-fluorite) crystals with the most intense line at... 

In section two of tUs paper we describe the technical aspects of C02-laser heating in a DAC. The third section focuses on the methods for measuring melting temperatures at variable pressures, the fourth section on the determination of high pressure and temperature phase diagrams, and in the fifth section some experiments focusing on the synthesis of diamond and cubic BN from organic precursors will be described. 

In CO2-laser heating experiments in a DAC it is important to eliminate sample temperature fluctuations due to fluctuations of the laser intensity. The peak-to-peak amplitude of the C02-laser power fluctuations in our experiments exceeded... 

C.-S. Yoo, J. Akella, and M. Nicol, Chemistry at high pressures and temperatures In-situ synthesis and characterization of P-Si3N4 by DAC X-ray/laser heating studies, in The 3rd NIRIM International Symposium on Advanced Materials (ISAM 96), M. Akaishi et al. (Eds), NIRIM, Tsukuba, Japan, 1996, pp. 175-179. 

The synthesis of a novel 7-813X4 phase with a cubic spinel structure (see Figure 2.1c) was carried out under high pressure (15 G Pa) and at temperatures above 1920 ° C in a laser-heated diamond cell [22]. Today, many different processing techniques for y-813X4 synthesis are available, the most common being the diamond anvil cell (DAC) synthesis (G. 8erghiou, et al., unpublished results), the multianvil pressure apparatus (MAP) synthesis [23], and the shock synthesis [24]. 

Schematics of the double-sided laser heating system combined with the SMS technique at sector 3 of the Advanced Photon Source [24], Two infrared laser beams are used to laser heat the sample in a DAC, whereas temperatures of the heated sample are measured by thermal radiation spectra fitted to Planck s function. The SMS signal is recorded by an avalanche photodiode detector in the forward direction. A stainless steel (SS) foil is used as a reference for deriving the CS of the iron sites.

Figure 3. Schematic drawing of the experimental set-up for the C02-Iaser heating experiments in a DAC 1=C02 laser, 2 = Si mirror, 3=ZnSe lens, 4=diamond cell, 5=reflecting objective, 6=monochromator, 7 = CCD detector, 8=PC, 9 and 12 = beam splitter, 10 = optical diode, 11 = regulating unit, 13 = ocular, 14=power supply of the CO2 laser. The dashed and dotted line shows the path of the C02-laser beam, the dash lines show the visible light path, and the solid ones depict electrical connections.

Figure 5. (a) Temperature fluctuations in the (Mg, Fe)SiOi sample heated in a DAC with an unstabilized CO2 laser 100 temperature measurements within a time interval of about 60s from the center of the heated area (squares). During this time interval the temperature fluctuated between 2140 and 3000 K. (b) Temperature fluctuations in the (Mg, Fe)Si03 sample heated in a DAC with laser stabilization to average temperatures of 2090 K. (diamonds), 2420 K (circles) and 3010 K (squares) were monitored during 35, 20, and 17 min, respectively. The laser stabilization suppressed the peak-to-peak fluctuations to below 120 K, or to below 5% of the average temperature. After [21]. 

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