Externally-heated Diamond Anvil Cell Research Articles

Thermal conductivity of aluminous garnets in Earth’s deep interior

Abstract Aluminous garnets [(Mg,Fe,Ca)3Al2(SiO4)3] are a key mineral group in Earth’s interior. Their thermal conductivity with relevant chemical compositions and at high-pressure-temperature (P-T) conditions plays a crucial role in affecting the thermal states of pyrolytic mantle and subducted basaltic crust over the depth range they are present. Using ultrafast optical pump-probe spectroscopy combined with an externally-heated diamond-anvil cell, we have precisely determined the high-P-T thermal conductivity of aluminous garnets, including pyrope, grossular, and pyrope-almandine solid solution. We find that the variable chemical composition has minor effects on the thermal conductivity of these garnets over the P-T range studied. Combined with previous results, we provide new depth-dependent thermal conductivity profiles for a pyrolytic mantle and a subducted basaltic crust. These results significantly benefit geodynamics simulations and advance our understanding of the thermal structure and evolution dynamics in Earth’s upper mantle and transition zone. In addition, as garnets are also a key, useful material family for modern technology, our results on the thermal property of natural garnets also shed light on the novel design of optical and electronic devices based on various synthetic nonsilicate garnets.

Novel non-Joule heating technique: Externally laser-heated diamond anvil cell

The externally heated diamond anvil cell (EHDAC) conducts high pressure and temperature experiments with spatial uniformity and temporal stability. These are conventionally combined with various spectroscopies and x-ray diffraction measurements. EHDAC techniques perform Joule heating on a heater placed close to or directly in contact with diamond anvils. However, the electrical wiring and heater required for Joule heating complicate EHDAC setups, hindering easy access for the measurement of physical properties. This study proposes an EHDAC technique using laser- instead of Joule-heating. We successfully achieved temperatures reaching 900 K by applying heat to diamond anvils through laser-heating of the gaskets with thermally insulating anvil seats. To test this setup, we measured the melting temperature of H2O ice VII, which was consistent with previous studies. We also measured the high-pressure and temperature impedance of H2O VII and verified the capability of electrical resistivity measurements in this setup. This technique allows various physical property measurements owing to its simple setup required for externally laser-heated diamond anvil cell experiments. The unique characteristics of this heating technique are that (1) no heaters or wiring are required, (2) it exhibits the most efficient heating among EHDAC studies, (3) it maintains the DAC body at room temperature, and (4) diamond anvils do not detach from anvil seats after the EHDAC experiment. This method significantly simplifies the experimental setup, which allows much easier access to various physical property measurements using an EHDAC.

SrB4O7:Sm2+ fluorescence improves the accuracy of temperature measurements in externally heated diamond anvil cells.

The sample temperature in an externally heated diamond anvil cell (EHDAC) is generally measured by a thermocouple fixed to the pavilions of diamond anvils, ignoring the temperature difference between the thermocouple and the sample. However, the measured temperature depends strongly on the placement of the thermocouple, thus seriously reducing the accuracy of the temperature measurement and hindering the use of EHDAC in experiments requiring precise temperature measurements, such as high-pressure melting and phase-diagram investigations. In this study, the full width at half maximum (FWHM) of the 0-0 fluorescence line of strontium borate doped with bivalent samarium ions (SrBO4:Sm2+, SBO) is found to be highly sensitive to temperature and responds extremely rapidly to small temperature fluctuations, which makes it an excellent temperature indicator. We propose herein a precise method to measure temperature that involves measuring the FWHM of the 0-0 fluorescence line of SBO. This method is used to correct the temperature discrepancy between the thermocouple and the sample in an EHDAC. These corrections significantly improve the accuracy of temperature measurements in EHDACs. The accuracy of this method is verified by measuring the melting point of tin at ambient pressure. We also use this method to produce a tentative elementary phase diagram of tin up to 109GPa and 495K. This method facilitates high-pressure, high-temperature experiments demanding accurate temperature measurements in various disciplines. The study also discusses, in general, the experimental approach to measuring temperature.

Phase Transitions in Natural Vanadinite at High Pressures

The structural stability of vanadinite, Pb5[VO4]3Cl, is reported by high-pressure experiments using synchrotron radiation X-ray diffraction (XRD) and Raman spectroscopy. XRD experiments were performed up to 44.6 GPa and 700 K using an externally-heated diamond anvil cell (EHDAC), and Raman spectroscopy measurements were performed up to 26.8 GPa at room temperature. XRD experiments revealed a reversible phase transition of vanadinite at 23 GPa and 600 K, which is accompanied by a discontinuous volume reduction and color change of the mineral from transparent to reddish during compression. The high-pressure Raman spectra of vanadinite show apparent changes between 18.0 and 22.8 GPa and finally become amorphous at 26.8 GPa, suggesting structural transitions of this mineral upon compression. The structural changes can be distinguished by the emergence of a new vibrational mode that can be attributed to the distortion of [VO4] and the larger distortion of the V–O bonds, respectively. The [VO4] internal modes in vanadinite give isothermal mode Grüneisen parameters varying from 0.149 to 0.286, yielding an average VO4 internal mode Grüneisen parameters of 0.202.

High-pressure thermal conductivity and compressional velocity of NaCl in B1 and B2 phase

Sodium chloride (NaCl) is an important, commonly used pressure medium and pressure calibrant in diamond-anvil cell (DAC) experiments. Its thermal conductivity at high pressure–temperature (P–T) conditions is a critical parameter to model heat conduction and temperature distribution within an NaCl-loaded DAC. Here we couple ultrafast optical pump-probe methods with the DAC to study thermal conductivity and compressional velocity of NaCl in B1 and B2 phase to 66 GPa at room temperature. Using an externally-heated DAC, we further show that thermal conductivity of NaCl-B1 phase follows a typical T−1 dependence. The high P–T thermal conductivity of NaCl enables us to confirm the validity of Leibfried-Schlömann equation, a commonly used model for the P–T dependence of thermal conductivity, over a large compression range (~ 35% volume compression in NaCl-B1 phase, followed by ~ 20% compression in the polymorphic B2 phase). The compressional velocities of NaCl-B1 and B2 phase both scale approximately linearly with density, indicating the applicability of Birch’s law to NaCl within the density range we study. Our findings offer critical insights into the dominant physical mechanism of phonon transport in NaCl, as well as important data that significantly enhance the accuracy of modeling the spatiotemporal evolution of temperature within an NaCl-loaded DAC.

A cylindrical SiC heater for an externally heated diamond anvil cell to 1500 K.

Semiconductor-based heaters for diamond anvil cells (DACs) have advantages over metal wire heaters in terms of repeated use and the ability to reach higher temperatures. We introduce a cylindrical SiC heater for an externally heated DAC (EHDAC) that works satisfactorily at temperatures up to 1500K and pressures around 90GPa. The heater is reusable and inexpensive, and only slight modifications to the DAC are required to fit the heater. Experiments on melting of NaCl and gold are conducted at ambient pressure to test the temperature accuracy of the EHDAC system, and resistance measurements on iodine at high pressures and temperatures are performed to assess the heater assembly. These test runs show that a uniform and accurate temperature can be maintained by the EHDAC assembly, which has potential applications to a variety of transport property measurements.

An Externally-Heated Diamond Anvil Cell for Synthesis and Single-Crystal Elasticity Determination of Ice-VII at High Pressure-Temperature Conditions.

The externally-heated diamond anvil cell (EHDAC) can be used to generate simultaneously high-pressure and high-temperature conditions found in Earth's and planetary interiors. Here we describe the design and fabrication of the EHDAC assemblies and accessories, including ring resistive heaters, thermal and electrical insulating layers, thermocouple placement, as well as the experimental protocol for preparing the EHDAC using these parts. The EHDAC can be routinely used to generate megabar pressures and up to 900 K temperatures in open air, and potentially higher temperatures up to ~1200 K with a protective atmosphere (i.e., Ar mixed with 1% H2). Compared with a laser-heating method for reaching temperatures typically >1100 K, external heating can be easily implemented and provide a more stable temperature at ≤900 K and less temperature gradients to the sample. We showcased the application of the EHDAC for synthesis of single crystal ice-VII and studied its single-crystal elastic properties using synchrotron-based X-ray diffraction and Brillouin scattering at simultaneously high-pressure high-temperature conditions.

An Externally-Heated Diamond Anvil Cell for Synthesis and Single-Crystal Elasticity Determination of Ice-VII at High Pressure-Temperature Conditions

An Externally-Heated Diamond Anvil Cell for Synthesis and Single-Crystal Elasticity Determination of Ice-VII at High Pressure-Temperature Conditions

Aqueous fluids as transport medium at high pressure and temperature: Ti4+ solubility, solution mechanisms, and fluid composition

The stability of Ti-bearing crystalline phases such as rutile and ilmenite in the Earth's interior can be dependent on the solubility behavior of TiO2 in aqueous fluids. Natural and experimental evidence indicate that significant TiO2 mobility is possible in this environment.Other solutes affect Ti solubility and solution mechanisms in the aqueous solutions. Here, the solubility behavior and the influence of other solutes on Ti solubility have been addressed with experiments in an externally-heated diamond anvil cell by using rutile coexisting with aqueous fluid in the TiO2-H2O, TiO2-SiO2-H2O, TiO2-(Na2O·5SiO2)-H2O, and TiO2-(CaO·5SiO2)-H2O systems in the 450–900 °C and 220–2100 MPa temperature and pressure range. Micro-Raman spectroscopy was employed to probe the samples while these were at the temperatures and pressures of interest.The TiO2 solubility in all fluid compositions studied increased with increasing temperature and pressure. The solubility is the lowest, between ~10 and ~50 ppm, in TiO2-H2O fluids. Addition of SiO2 enhances the TiO2 solubility to concentration in excess of 150 ppm at the highest temperature and pressure (900 °C/1335 MPa). The solubility in TiO2-(Na2O·5SiO2)-H2O, and TiO2-(CaO·5SiO2)-H2O fluids is more than twice that in TiO2-SiO2-H2O fluids. The TiO2 solubility in the Na-system is about 50 ppm greater than in the Ca-system. The enthalpy of solution of TiO2 in the aqueous fluids is in the 15–28 kJ/mol range.The local oxygen environment surrounding Ti4+ in TiO2-H2O and TiO2-SiO2-H2O fluids resembles that in the rutile structure (i.e., 6-coordinated Ti4+). With Na+ or Ca2+ in the fluid, additional complexes are formed with a smaller number of oxygen in the coordination sphere.The bulk composition of hydrated rocks in the Earth's interior governs the pressure/temperature-stability of hydrous phases and, therefore, solute content of a fluid released when the stability limits of the hydrous phases in the rocks are exceeded and aqueous fluid is released. This solute and, therefore, the source rock bulk composition, controls titanium solubility. For example, the distribution of Ti-bearing phases in equilibrium with aqueous fluid in subduction zone environments depends on the depth and thermal profile because the temperature and pressure stability of the relevant hydrous minerals (e.g., serpentine, lawsonite, hornblende, phengite) are quite different.

Phase transition and thermoelastic behavior of cadmium sulfide at high pressure and high temperature

The phase transition and thermal equation of state of cadmium sulfide (CdS) were studied at high pressure and temperature conditions up to 21.9 GPa and 650 K, by using in situ synchrotron angle-dispersive X-ray diffraction and an externally-heated diamond anvil cell (DAC). A pressure-induced phase transition from wurtzite structure (WZ) to rocksalt structure (RS) was observed at about 2.6 GPa, which was agreed with previous studies (2.0–3.5 GPa). In addition, fitting of the experimental data by means of the third-order Brich-Murnaghan equation of state (III-BM EoS) gives the bulk modulus K0 = 81.6 (13) GPa, its pressure derivative K′0 = 3.68 (13), and the volumetric thermal expansion coefficient α0 = 2.97 (25) × 10−5 K−1 for RS phase of CdS. Simultaneously, the thermal expansion coefficient (α0 = 1.51 × 10−5 K−1), and its axial thermal expansivities (8.30 × 10−6 K−1 and 5.96 × 10−6 K−1) along a-axis and c-axis for WZ phase of CdS at ambient conditions were obtained, respectively. Moreover, it was found that the phase transition pressure from WZ (or ZB) type to RS type of cadmium chalcogenides (CdS, CdSe and CdTe) is quite similar by comparing their phase transition pressures. Furthermore, the elastic properties of metal sulfides (ZnS, CdS, HgS, PbS) with the same crystal structure but different metal cations were also discussed, and found that the bulk moduli for the RS phase of metal sulfides (ZnS, CdS, HgS, PbS) have a negative correlation with the cation radius, but a positive correlation with the electronegativity.

In situ study of the fractionation of hydrogen isotopes between aluminosilicate melts and coexisting aqueous fluids at high pressure and high temperature – Implications for the δD in magmatic processes

The hydrogen isotopic composition of melt inclusions trapped in phenocrysts during their crystallization and growth in a magma may contribute to a better understanding of the water cycle between the atmosphere, the hydrosphere and the lithosphere. Such understanding relies on the knowledge of the hydrogen isotopic fractionation factors between aqueous fluids, silicate melts, and minerals at temperature and pressure conditions relevant to the Earth's interior. Significant D/H fractionation between silicate melts and aqueous fluids was reported at hundreds of MPa and °C by using in situ measurements in hydrothermal diamond anvil cell (HDAC) experiments (Mysen, 2013a, 2013b, Am. Mineral. 98, 376–386 and 1754–1764). However, the available dataset is focused on fluids and melts with D/H ratios close to unity. The relevance of such data for natural processes that involve per mil variations of δD-values may not always be clear. To address such concerns, the effect of the bulk D/H ratio on hydrogen isotope partitioning between water-saturated silicate melts and coexisting silicate-saturated aqueous fluids has been determined in the Na2O–Al2O3–SiO2–H2O–D2O system. To this end, in situ Raman spectroscopic measurements were performed on fluids and melts with bulk D/H ratios from 0.05 to 2.67 by using an externally-heated diamond anvil cell in the 300–800 °C and 200–1500 MPa temperature and pressure range, respectively.In these pressure/temperature ranges, the D/H ratios of fluids in equilibrium with melt barely change with temperature (in average ΔHfluid=0.47±1.15 kJ/mol). In contrast, the D/H ratios of coexisting melts display strong dependence on temperature (average ΔHmelt=7.18±1.27 kJ/mol). The temperature-dependence of the D/H fractionation factor between melt and fluid (αfluid-melt=D/Hfluid/D/Hmelt) is comparable in all the experiments and can be written: 1000⋅ln⁡(αfluid-melt)=263(±26)⋅T−2–126(±48). Therefore, the αfluid-melt is independent of the bulk D/H ratio of the melt + fluid system.Experimentally determined αfluid-melt using D-enriched fluids, therefore, can be applied to natural systems. It follows that for water-saturated magma strong isotopic fractionation of D and H between water dissolved in magmas and deep aqueous fluids may occur. The δD-values in melt inclusions in phenocrysts in such water-saturated magma will reflect such fluid/melt fractionation effects. A likely result is underestimation of the δD isotopic composition of slab fluids based on δD-values in melt inclusions. The temperature-dependent hydrogen isotope fractionation must be taken into account in the modeling of slab fluid–magma interaction in the mantle wedge.

Sound velocities of bcc-Fe and Fe0.85Si0.15 alloy at high pressure and temperature

Studying the velocity–density profiles of iron and iron–silicon alloy at high pressures and temperatures is critical for understanding the Earth’s core as well as the interiors of other planetary bodies. Here we have investigated the compressional wave velocity (VP) and density (ρ) profiles of polycrystalline bcc-Fe and Fe0.85Si0.15 alloy (8wt.% Si) using in situ high-energy resolution inelastic X-ray scattering (HERIX) and synchrotron X-ray diffraction spectroscopies in an externally-heated diamond anvil cell (EHDAC) up to 15GPa and 700K. Based on the measured velocity–density (VP–ρ) and velocity–pressure (VP–P) relations of bcc-Fe at simultaneous high pressure and temperature (P–T) conditions, our results show a strong VP reduction at elevated temperatures at a constant density. Comparison of the VP–ρ profiles between the bcc-Fe and bcc-Fe0.85Si0.15 alloy indicates that the alloying effect of additional 8wt.% Si on the VP–ρ relationship of bcc-Fe is predominant via a constant density decrease of approximately 0.6g/cm3 (7%). Compared with the literature velocity results for bcc and hcp Fe–Si alloys, the bcc-Fe and Fe–Si alloys exhibit higher VP than their hcp phase counterparts at the given bcc–hcp transition pressures. Our results here strongly support the notion that high temperature has a strong effect on the VP of Fe and that the VP–ρ profile of Fe can be affected by structural and magnetic transitions. Analyses on literature elastic constants of the bcc Fe–Si alloys, as a function of P–T and Si content, show that the bcc phase displays extremely high VP anisotropy of 16–30% and VS splitting anisotropy of 40–90% at high temperatures, while the addition of Si further enhances the anisotropy. Due to the extremely high elastic anisotropy of the bcc Fe–Si alloy, a certain portion of the bcc Fe–Si alloy with the lattice-preferred orientation may produce VP and VS anisotropies to potentially account for the observed seismic anisotropy in the inner core.

Elasticity of single-crystal iron-bearing pyrope up to 20 GPa and 750 K

Elastic properties of the major constituent minerals in the Earth's upper mantle at relevant high pressure–temperature (P–T) conditions are crucial for understanding the composition and seismic velocity structures of this region. In this study, for the first time, we have measured the single-crystal elasticity of natural Fe-bearing pyrope, Mg2.04Fe0.74Ca0.16Mn0.05Al2Si3O12, using in situ Brillouin spectroscopy and X-ray diffraction at simultaneous high P–T conditions up to 20GPa and 750K in an externally-heated diamond anvil cell. The derived aggregate adiabatic bulk and shear moduli (KS0, G0) at ambient conditions are 168.2 (±1.8)GPa (the value in parentheses represents propagated uncertainties ±1σ) and 92.1 (±1.1)GPa, respectively, consistent with literature results. Using the third-order Eulerian finite-strain equation to model the high P–T data, the derived pressure derivatives of the bulk and shear moduli at constant temperature are (∂KS/∂P)T=4.4 (±0.1) and (∂G/∂P)T=1.2 (±0.1), respectively, whereas the temperature derivatives of these moduli at constant pressure are (∂KS/∂T)P=−16.8 (±1.3)MPa/K and (∂G/∂T)P=−5.1 (±1.1)MPa/K, respectively. Compared to literature values, our results show that addition of 25mol% Fe in pyrope increases the pressure derivative of the bulk modulus by 7%, but has a negligible effect on other elastic parameters. Extrapolation of our results shows that Fe-bearing pyrope remains almost elastically isotropic at relevant P–T conditions of the upper mantle, indicating that it may not have a significant contribution to seismic VP and VS anisotropy in the upper mantle. Together with the elasticity of olivine and pyroxene minerals in the upper mantle, we have constructed new velocity profiles for two representative compositional models, pyrolite and piclogite, along a representative geotherm of the Earth's upper mantle. These velocity models show VS profiles consistent with seismic observations, although VP profiles are slightly lower than global seismic observations. Our analyses also show that approximately 30% garnet in a mineralogical model is needed to best match both seismic VP and VS profiles of the region, although such high garnet content needs to be reconciled with our current geochemical understanding. Our results here provide new insights into seismic profiles and mineralogical models of the upper mantle region.

Sound velocities of hydrous ringwoodite to 16 GPa and 673 K

To understand the effect of hydration on the sound velocities of major mantle minerals and to constrain the mantle's H2O budget, we have measured the single-crystal elastic moduli of hydrous ringwoodite, (Mg1.633Fe2+0.231Fe3+0.026)Si1.00H0.179O4 with 1.1wt.% H2O using Brillouin scattering combined with X-ray diffraction in an externally-heated diamond anvil cell up to 16GPa and 673K. Up to 12GPa at 300K, the presence of 1.1wt.% H2O lowers the elastic moduli of ringwoodite by 5–9%, but does not affect the pressure derivatives of the elastic moduli compared to anhydrous ringwoodite. The reduction caused by hydration is significantly enhanced when temperatures are elevated at high pressures. At 12GPa, increasing temperature by ΔT=100K leads to a 1.3–2.4% reduction in the elastic moduli (C11, C12, and C14). Comparing our results with seismic observations, we have evaluated the potential H2O content in the lower part of the transition zone. Our results indicate that the observed seismic velocity anomalies and related depth depression of the 660-km discontinuity could be attributed to thermal variations together with the presence of ~0.1wt.% H2O.

The origin of the negative niobium tantalum anomaly in subduction zone magmas

In order to determine the distribution of niobium and tantalum between clinopyroxenes and aqueous fluids, we measured in two separate sets of experiments niobium and tantalum solubility in clinopyroxenes and in aqueous fluids, respectively. The solubility of niobium in clinopyroxenes was experimentally investigated in the system CaMgSi2O6–NaAlSi2O6–Nb2O5–H2O at 1.5 GPa and 700–1100 °C using piston-cylinder experiments. In the presence of excess Nb2O5, CaNb2O6 coexists with a clinopyroxene. The solubility of niobium in the pyroxene increases drastically with the aluminum content. While the solubility of niobium is in the order of 100–300 ppm by weight for Al-poor clinopyroxenes, it reaches 4 wt.% for clinopyroxenes containing 10 wt.% Al2O3. Microprobe analyses suggest that Nb is incorporated in the clinopyroxene as NaNbAl2O6 component. The solubility of CaNb2O6 in aqueous fluid was determined by the direct visual observation of the dissolution of CaNb2O6 crystals in an aqueous fluid using an externally-heated diamond anvil cell. At 1.5 to 1.7 GPa and 800–1000 °C, an aqueous fluid saturated with diopside dissolves only 20–100 ppm by weight of CaNb2O6, i.e. niobium solubility in the fluid is orders of magnitude below the solubility in aluminous clinopyroxenes. Experiments on the solubility of CaTa2O6 in clinopyroxenes and in aqueous fluid suggest that Ta behaves generally similar to Nb, but with the notable exception that the solubility of CaTa2O6 in aqueous fluids and aluminous pyroxenes is approximately a factor of five lower than the solubility of the corresponding niobium compound. Our results imply that (1) the fluid/clinopyroxene partition coefficient for Nb and Ta is between 0.1 and 0.001 for aqueous fluids containing little dissolved silicates and for clinopyroxenes of a composition realistic for the subducted slab or the subarc mantle. Only for very Al-poor clinopyroxenes may the partition coefficient approach unity. (2) The depletion of Nb and Ta in subduction zone magmas and fluids is related to the intrinsically low solubility of Nb and Ta in water-rich and solute-poor fluids in the shallow parts of a subduction zone. (3) The presence of rutile in the subducted slab is not a necessary requirement for the development of the negative Nb and Ta anomaly. (4) Fluid transport of niobium and tantalum will affect the Nb/Ta ratio in the subarc mantle only under exceptional circumstances. (5) Previous reports of high fluid/clinopyroxene partition coefficients for Nb and Ta are probably related to the Al-free or Al-poor composition of the systems studied.

Simultaneous volume measurements of post-perovskite and perovskite in MgSiO 3 and their thermal equations of state

Simultaneous volume measurements of MgSiO 3 post-perovskite (PPv) and perovskite (Pv) were performed in a diamond anvil cell (DAC) combined with synchrotron X-rays. An externally-heated DAC was used in addition to a laser-heated DAC for the volume measurement experiment at high temperatures. The volume data were collected in the stability field of post-perovskite from 115 to 130 GPa. The temperature generated in the externally-heated and the laser-heated DACs for the volume measurement were up to 832 and 2330 K, respectively. Using two different but complementary heating techniques, we collected the data at a wide temperature range from 300 to 2330 K. The obtained P-V-T data for PPv and Pv were fitted to a third-ordered Birch-Murnaghan equation of state (EOS). For a precise comparison of the volume between the two phases, the EOSs were constructed based on the same pressure scale of MgO. The simultaneous volume measurements and the volumes calculated from the determined EOSs demonstrate that the volume difference between PPv and Pv of about 1.5% is almost constant with increasing temperature to 4000 K at the transition. At the base of the mantle, this density difference corresponds to a temperature anomaly of 1300 K without the phase transition due to the very small thermal expansivity of minerals, which has a significant effect on mantle dynamics. The thermal expansivity contrast between the top and the bottom of the mantle is a factor of 3.6. From a mantle convection study, this value suggests that huge and hot plumes are formed at the core–mantle boundary.

Phase transition in CaSiO 3 perovskite

A phase transition in pure CaSiO 3 perovskite was investigated at 27 to 72 GPa and 300 to 819 K by in-situ X-ray diffraction experiments in an externally-heated diamond-anvil cell. The results show that CaSiO 3 perovskite takes a tetragonal form at 300 K and undergoes phase transition to a cubic structure above 490–580 K in a pressure range studied here. The transition boundary is strongly temperature-dependent with a slightly positive d T / d P slope of 1.1 (± 1.3) K/GPa. It is known that the transition temperature depends on Al 2O 3 content dissolved in CaSiO 3 perovskite [Kurashina et al., Phys. Earth Planet. Inter. 145 (2004) 67–74]. The phase transition in CaSiO 3(+ 3 wt.% Al 2O 3) perovskite therefore could occur in a cold subducted mid-oceanic ridge basalt (MORB) crust at about 1200 K in the upper- to mid-lower mantle. This phase transition is possibly ferroelastic-type and may cause large seismic anomalies in a wide depth range.

Melting of indium at high pressure determined by monochromatic x-ray diffraction in an externally-heated diamond anvil cell

The melting behavior of indium at high pressure has been studied in an externally heated diamond anvil cell (DAC) using x-ray diffraction measurements. Melting at high pressure was identified by the appearance of diffuse scattering from the melt with the simultaneous disappearance of crystalline diffraction signals. The observed melting curve is in good agreement with previous determinations based on resistivity measurements in a piston cylinder apparatus. These results demonstrate the successful melting experiments in a DAC using the x-ray diffuse scattering as the melting criterion.

Experimental studies of Earth's deep interior: accuracy and versatility of diamond-anvil cells

Phase equilibria, chemical reactions, equations of state and elasticity investigated at high P-T in candidate materials for the mantle and the core provide an experimental basis for modelling the structure, dynamics and evolution of the Earth's deep interior. During the past three decades, diamond-anvil cells have been developed for experimental simulation of the pressure conditions of the entire Earth in the laboratory. Simultaneous high temperatures have been generated with various heating techniques. Physical and chemical properties of materials have been determined in situ at high P-T with microsampling techniques. Further improvements in accuracy and versatility of these measurements are essential for resolving key geophysical problems. Some recent developments in our laboratory are summarized, and assessments of the present status and immediate future of the field are offered.

Melting criteria and imaging spectroradiometry in laser-heated diamond-cell experiments

As a step toward resolving current discrepancies among ultrahigh-pressure melting curves obtained with the laser-heated diamond cell, we critically evaluate two aspects of the experiments that require further examination: (i) the criteria used to detect that melting has taken place, and (ii) the methods employed for measuring spatially variable temperatures. A review of recent efforts illustrates how defining reliable melting criteria remains problematical in many experiments, whereas current and prospective advances in imaging spectroradiometry can yield robust methods for determining the temperature distribution within the laser-heated diamond cell.