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Abstract: The temperature at the 410-km discontinuity is re-evaluated by comparing the depth of the discontinuity with the olivine–wadsleyite transition pressure obtained using in situ X-ray diffraction experiments by and equation of state (EoS) of MgO by (Tange scale) and . The newly estimated temperature is 1830±48K, 70K higher than that by our previous estimation. The EoSes of the major mantle minerals (olivine, wadsleyite, ringwoodite and perovskite) are also recalculated using the Tange scale. The adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these EoSes. The adiabatic temperature gradient gradually decreases with increasing depth without a phase transition, and abruptly increases in association with phase transitions. The adiabatic temperature gradients are found to be 04–0.5 and 0.3K/km in the upper and lower parts of the mantle, respectively. The temperatures at a depth of 200km, the bottom of the mantle transition zone, the top of the lower mantle and a depth of 2700km are found to be 1720±40, 2010±40, 1980±40, and 2730±50K. The mantle potential temperature is found to be 1610±35K. [ABSTRACT FROM AUTHOR]

Abstract: Volumes of forsterite were measured by in situ X-ray diffraction at simultaneously high pressures and high temperatures up to 14GPa and 1900K in a Kawai-type multi-anvil apparatus. By fitting the present data to the Mie-Grüneisen-Debye thermal equation of state with the results of the previous reliable studies, we obtained γ 0 =1.31(1) and q =3.2(1). The logarithmic volume dependence of the thermal expansion coefficient was found to be δ T =8.4(2). The average temperature derivative of the isothermal bulk modulus in the investigated pressure–temperature ranges was found to be (∂K T /∂T) P =−0.028(1)GPa/K. The isobaric heat capacity and thermal pressure at high pressure and high temperature were estimated using the present volume data. The adiabatic geotherm at the top and base of the uppermost mantle are 0.60(2) and 0.34(2)K/km. The temperature estimated from the 410-km discontinuity depth and the olivine-wadsleyite transition pressure suggests a mantle potential temperature of 1520±40K. [Copyright &y& Elsevier]

The phase boundary of the post-spinel transition in Mg2SiO4 was re-investigated by means of high P–T in situ X-ray diffractometry with a gold pressure marker in a Kawai-type apparatus. Rapid and continuous temperature changes were conducted to initiate dissociation of spinel, which tends to be inert after long annealing. Isothermal decompression at high temperature was conducted to form spinel from perovskite plus periclase. The phase boundary is located at ca. 22 GPa in the temperature range from 1550 to 2100 K, which is 1–1.5 GPa lower than the 660 km discontinuity. This discrepancy might be explained in terms of the pressure effect of thermocouple emf and inaccurate equation of state (EOS) for the pressure maker. The transition is found to be less sensitive to temperature than reported previously, with a Clapeyron slope ranging from −2 to −0.4 MPa/K. This small Clapeyron slope implies that the post-spinel transition would not be an effective barrier to mantle convection. [Copyright &y& Elsevier]

The Clapeyron slope is the slope of a phase boundary in P–T space and is essential for understanding mantle dynamics and evolution. The phase boundary is delineating instead of balancing a phase transition's normal and reverse reactions. Many previous high pressure–temperature experiments determining the phase boundaries of major mantle minerals experienced severe problems due to instantaneous pressure increase by thermal pressure, pressure drop during heating, and sluggish transition kinetics. These complex pressure changes underestimate the transition pressure, while the sluggish kinetics require excess pressures to initiate or proceed with the transition, misinterpreting the phase stability and preventing tight bracketing of the phase boundary. Our recent study developed a novel approach to strictly determine phase stability based on the phase equilibrium definition. Here, we explain the details of this technique, using the post-spinel transition in Mg2SiO4 determined by our recent work as an example. An essential technique is to observe the change in X-ray diffraction intensity between ringwoodite and bridgmanite + periclase during the spontaneous pressure drop at a constant temperature and press load with the coexistence of both phases. This observation removes the complicated pressure change upon heating and kinetic problem, providing an accurate and precise phase boundary. [ABSTRACT FROM AUTHOR]

Penetrating, high‐energy synchrotron X‐rays are in strong demand, particularly for high‐pressure research in physics, chemistry and geosciences, and for materials engineering research under less extreme conditions. A new high‐energy wiggler beamline P61 has been constructed to meet this need at PETRA III in Hamburg, Germany. The first part of the paper offers an overview of the beamline front‐end components and beam characteristics. The second part describes the performance of the instrumentation and the latest developments at the P61B endstation. Particular attention is given to the unprecedented high‐energy photon flux delivered by the ten wigglers of the PETRA III storage ring and the challenges faced in harnessing this amount of flux and heat load in the beam. Furthermore, the distinctiveness of the world's first six‐ram Hall‐type large‐volume press, Aster‐15, at a synchrotron facility is described for research with synchrotron X‐rays. Additionally, detection schemes, experimental strategies and preliminary data acquired using energy‐dispersive X‐ray diffraction and radiography techniques are presented. [ABSTRACT FROM AUTHOR]

To determine the phase boundary between the perovskite and post-perovskite structures in MnGeO3, in situ X-ray observations were carried out at pressures of 57-68 GPa and temperatures of 1000-1900 K using the Kawai-type high-pressure apparatus equipped with sintered diamond anvils interfaced with synchrotron radiation. The phase boundary was determined to be P (GPa) = 39.2 + 0.013T (K) based on Tsuchiya's (2003) gold pressure scale. The Clapeyron slope, dP/dT, of 13(+12/-5) MPa/K, determined in the present study is larger that of MgGeO3 and MgSiO3. [ABSTRACT FROM AUTHOR]

We investigated phase relations in pyrolite at ∼33-40 GPa and ∼1800-2150 K by in situ X-ray diffraction using Kawai-type apparatus with sintered diamond anvils. The results demonstrated that MgSiO3-rich orthorhombic perovskite (mpv), CaSiO3-rich cubic perovskite (cpv) and (Mg,Fe)O ferropericlase (fp) are the stable phases in pyrolite bulk composition at the conditions corresponding to the lower mantle. However, chemical analyses of a run product recovered from ∼ 34 GPa by an analytical transmission electron microscope showed the coexistence of metallic iron particles with mpv, fp, and SiO2-rich amorphous phase. Also, Fe/Mg partitioning coefficient between mpv and fp was found to be 0.66(31), which is consistent with previous results for pyrolite bulk composition at 26-30 GPa and ∼1900 K. These results indicate that iron-rich metallic particles can exist in the lower mantle as a stable phase to the depth of at least ∼900 km. [ABSTRACT FROM AUTHOR]

The phase relations of iron-rich olivine and its high-pressure polymorphs are important for planetary science and meteoritics because these minerals are the main constituents of terrestrial mantles and meteorites. The olivine–ahrensite binary loop was previously determined by thermochemical calculations in combination with high-pressure experiments; however, the transition pressures contained significant uncertainties. Here we determined the binary loop of the olivine–ahrensite transition in the (Mg,Fe)2SiO4 system at 1740 K in the pressure range of 7.5–11.2 GPa using a multi-anvil apparatus with the pressure determined using in situ X-ray diffraction, compositional analysis of quenched run products, and thermochemical calculation. Based on the determined binary loop, a user-friendly software was developed to calculate pressure from the coexisting olivine and ahrensite compositions. The software is used to estimate the shock conditions of several L6-type chondrites. The obtained olivine–ahrensite phase relations can also be applied for precise in-house multi-anvil pressure calibration at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract: The solid solutions of strontium–calcium phosphate, γ-Ca3−x Sr x (PO4)2 (0≤ x ≤2), have been synthesized under high-pressure and high-temperature conditions. The products were well characterized by powder X-ray diffraction measurements and Micro-Raman spectroscopy. All the products are isostructural and belong to R-3m space group. With the increasing content of Sr in γ-Ca3−x Sr x (PO4)2, the unit cell parameters (a, c, c/a, V) linearly increase, and the wavenumbers of Raman vibrational modes (v 3, v 1, v 4, v 2) also change in linear trends with different slopes. [Copyright &y& Elsevier]

Thermal expansion of synthetic coesite was studied with synchrotron powder X-ray diffraction in the temperature range of 100-1000 K. We determined the unit cell parameters of monoclinic coesite (a, b, c, and β) every 50 K in this temperature range. We observed that a and b parameters increase with increasing temperature, while c decreases. The β angle also decreases with temperature and approaches 120°. As a result, the unit cell volume expands by only 0.7% in this temperature range. Our measurements provide thermal expansion coefficients of coesite as a function of temperature: it increases from 3.4 × 10−6 K−1 at 100 K to 9.3 × 10−6 K−1 at 600 K and remains nearly constant above this temperature. The Suzuki model based on the zero-pressure Mie-Grüneisen equation of state was implemented to fit the unit cell volume data. The refined parameters are V0 = 546.30(2) Å3, Q = 7.20(12) × 106 J/mol and θD = 1018(43) K, where θD is the Debye temperature and V0 is the unit cell volume at 0 K with an assumption that K′ is equal to 1.8. The obtained Debye temperature is consistent with that determined in a previous study for heat capacity measurements. [ABSTRACT FROM AUTHOR]

We have expanded the pressure ranges at room and high temperatures generated in a Kawai-type multi-anvil apparatus (KMA) using tungsten carbide (WC) anvils with a high hardness ofHv = 2700 and a Young’s modulus of 660 GPa. At room temperature, a pressure of 64 GPa, which is the highest pressure generated with KMA using WC anvils in the world, was achieved using 1°-tapered anvils with a 1.5-mm truncation. Pressures of 48–50 GPa were generated at high temperatures of 1600–2000 K, which are also higher than previously achieved. Tapered anvils make wide anvil gaps enabling efficient X-ray diffraction. The present pressure generation technique can be used for studying the upper part of the Earth’s lower mantle down to 1200 km depth without sintered diamond anvils. [ABSTRACT FROM PUBLISHER]

The high-temperature clinoenstatite (HT-CEn) is one of the most important MgSiO3 pyroxene polymorphs, but the details of its structure and stability have been uncertain. The single crystal of the C2/ c HT-CEn end-member is firstly synthesized by rapid pressure-temperature quenching from 15-16 GPa and 1173-2173 K. The single-crystal X-ray diffraction analysis shows unusual bonding distances and static disorder of the atoms frozen in this metastable structure. The degree of kinking of the silicate tetrahedral chains is 175° for HT-CEn. The chain angle for HP-CEn is substantially smaller (135°), but the angle for L-CEn is in the opposite direction at −160° (= 200°). The degree of kinking increases by being curved by more than 180° for the transition from HT-CEn to L-CEn. As for the reverse change from the expansion to the stretch, a potential barrier exists at the point of the continuity. It is suggested that the reason why a structure can be quenched under ambient conditions is as follows: the present HT-CEn single crystal has been formed by the isosymmetric phase transition from the high-pressure C2/ c clinoenstatite (HP-CEn). The presence of HT-CEn from HP-CEn in natural rocks is an indicator of quenching history, which leads to the possibility that it exists in shocked meteorites and impact materials. [ABSTRACT FROM AUTHOR]

Abstract: High pressure generation has been tried by using the Kawai-cell equipped with sintered diamond cubes and the synchrotron radiation at SPring-8. The maximum attainable pressure reached 90.4GPa at 300K based on the Anderson et al. (1989) Au scale. Simultaneously, we investigated the perovskite (Pv)–postperovskite (PPv) transformation in MgGeO3 up to ca. 74GPa and 2200K by means of in situ X-ray diffraction method. Transformation from Pv to PPv was observed at pressures and temperatures higher than 63GPa and 1300K. Both the forward and the reverse reactions were found to be fairly sluggish over the examined temperature range. We determined the phase boundary by passing through the conditions at which either Pv or PPv phase grew and that of coexistence of both the phases, which is expressed by the equation T(K)=177 P(GPa)−9677. Our dP/dT slope of 5.6MPa/K for MgGeO3 is close to the minimum estimate for MgSiO3 and accordingly suggests relatively deeper D″ discontinuity and a high heat flux from the core. We emphasize that the phase boundary completely relies on the pressure scale adopted. [Copyright &y& Elsevier]