Papers by Przemyslaw Dera
High Pressure Research, 2008
ABSTRACT Double-sided laser heating combined with synchrotron x-ray radiation for in-situ studies... more ABSTRACT Double-sided laser heating combined with synchrotron x-ray radiation for in-situ studies in the DAC using diffraction, emission and inelastic scattering methods has been the most productive and widely used high temperature-high pressure technique in past two decades. Equation of state, phase transformations, element partitioning, electronic and optical properties of various materials have been successfully studied at conditions relevant to the Earth's interior with help of lasers. High temperature data collected in the DAC are mostly consistent, however, there are some discrepancies in reported results among high pressure research groups performing experiments at different facilities, particularly for determinations of melting temperatures, Clapeyron slopes, elastic constants, and thermal expansion coefficients. Although differences in the samples themselves cannot be ruled out, an important contributor to inconsistent results is related to temperature non-uniformity in the analyzed volume. Here we report a new development in on-line, double-sided, laser heating systems based on diode pumped fiber lasers coupled with beam-shaping optics that allows control of the shape of the focused laser beam spot on the sample surface in the DAC with variable diameter from 8 to 40 mum. Varying the settings of the laser heating system, we were able to shape the beam to almost any desired intensity profile and size on the surface of the sample in the DAC including tight focus, flat top, trident and doughnut types. The significant advantages and excellent performance of the flat top laser heating (FTLH) technique will be demonstrated in melting experiments on germanium and iron compounds. During FT laser heating the molten sample doesn't escape from the homogeneously heated area as is usually observed for Gaussian or doughnut type laser spots in the DAC. The capability to maintain the molten sample in the DAC for a relatively long time (at least 60 s) allowed us to collect high quality x-ray scattering data suitable for structure analysis even from low-Z molten materials such as Si, SiO2, Fe, Fe:C etc. The FT-LH method opens a new era in high temperature high pressure studies using diamond anvil cell with combination of advanced synchrotron as well as lab techniques, and will lead to superior quality high temperature measurements including equation of state, melting curve, phase transformation, element portioning, elastic, electronic and optical properties.
American Mineralogist, 2003
The stability and properties of carbonates at mantle conditions are of great importance for the c... more The stability and properties of carbonates at mantle conditions are of great importance for the carbon cycle, controlling the fate of subducting carbonate rich crust and mantle fertilization processes. Theoretical and experimental observations indicate that magnesite is the product of reaction of carbonates with silicate minerals, and it has been found to be stable within lower mantle conditions. A siderite
Proceedings of the National Academy of Sciences, 2004
The electronic spin state of iron in lower mantle perovskite is one of the fundamental parameters... more The electronic spin state of iron in lower mantle perovskite is one of the fundamental parameters that governs the physics and chemistry of the most voluminous and massive shell in the Earth. We present experimental evidence for spin-pairing transition in aluminum-bearing silicate perovskite (Mg,Fe)(Si,Al)O 3 under the lower mantle pressures. Our results demonstrate that as pressure increases, iron in perovskite transforms gradually from the initial high-spin state toward the final low-spin state. At 100 GPa, both aluminum-free and aluminum-bearing samples exhibit a mixed spin state. The residual magnetic moment in the aluminum-bearing perovskite is significantly higher than that in its aluminum-free counterpart. The observed spin evolution with pressure can be explained by the presence of multiple iron species and the occurrence of partial spin-paring transitions in the perovskite. Pressure-induced spin-pairing transitions in the perovskite would have important bearing on the magne...
Proceedings of the National Academy of Sciences, 2013
Knowledge of the structural properties of mantle phases is critical for understanding the enigmat... more Knowledge of the structural properties of mantle phases is critical for understanding the enigmatic seismic features observed in the Earth’s lower mantle down to the core–mantle boundary. However, our knowledge of lower mantle phase equilibria at high pressure ( P ) and temperature ( T ) conditions has been based on limited information provided by powder X-ray diffraction technique and theoretical calculations. Here, we report the in situ single-crystal structure determination of (Mg,Fe)SiO 3 postperovskite (ppv) at high P and after temperature quenching in a diamond anvil cell. Using a newly developed multigrain single-crystal X-ray diffraction analysis technique in a diamond anvil cell, crystallographic orientations of over 100 crystallites were simultaneously determined at high P in a coarse-grained polycrystalline sample containing submicron ppv grains. Conventional single-crystal structural analysis and refinement methods were applied for a few selected ppv crystallites, which ...
Journal of Solid State Chemistry, 2000
The crystal structure of Ba 4 Ru 3 O 10 has been determined by single-crystal X-ray di4raction at... more The crystal structure of Ba 4 Ru 3 O 10 has been determined by single-crystal X-ray di4raction at room pressure. From re5nements to R ؍ 0.0203 at room temperature and ambient pressure, the material is orthorhombic with space group Cmca (space group No. 64) and has lattice parameters of a ؍ 5.7762(15) A s , b ؍ 13.271(4) A s , and c ؍ 13.083(3) A s. The unit cell thus has a volume of V ؍ 1002.9(8) A s 3 and contains four formula units (Z ؍ 4). Ba 4 Ru 3 O 10 is therefore of higher symmetry than the previously reported monoclinic structure based on powder X-ray data. It is isostructural with the quaternary oxides Ba 4 (Ti, Pt) 3 O 10 and Ba 4 Ir 2 AlO 10 and the ternary 6uorides Cs 4 M 3 F 10 (M ؍ Mg, Co, Ni, Zn). Kinked chains of RuO 6 octahedra run along the c direction, consisting of sets of three face-sharing units joined at the corners of the end units to additional similar sets. The two distinct Ba sites show 10-fold and 11-fold coordination. Compressibilities and bulk modulus have been determined from lattice parameter variations at pressures up to 5.4 GPa. No phase transition was observed up to this pressure. Compressibility is greatest along the c axis and the bulk modulus obtained from a weighted 5t to a Vinet equation of state is 113.3(47) GPa.
Journal of Physics: Condensed Matter, 2005
Journal of Geophysical Research, 2009
High-pressure and high-temperature behavior of synthetic Ni 2 P has been studied in a laser-heate... more High-pressure and high-temperature behavior of synthetic Ni 2 P has been studied in a laser-heated diamond anvil cell up to 50 GPa and 2200 K. Incongruent melting associated with formation of pyrite-type NiP 2 and amorphous NiP alloy was found at an intermediate pressure range, between 6.5 and 40 GPa. Above 40 GPa, Ni 2 P melts congruently. At room conditions, Ni 2 P has hexagonal C22-type structure, and without heating it remains in this structure to at least 50 GPa. With a bulk modulus K 0 = 201(8) GPa and K' = 4.2(6), Ni 2 P is noticeably less compressible than hcp Fe, as well as all previously described iron phosphides, and its presence in the Earth core would favorably lower the core density. In contrast to Fe 2 P, the c/a ratio in Ni 2 P decreases on compression because of the lack of ferromagnetic interaction along the c direction. Lack of the C22!C23 transition in Ni 2 P rules out a stabilizing effect of Ni on the orthorhombic phase of natural (Fe 1Àx Ni x) 2 P allabogdanite.
High Pressure Research, 2008
Laser heating plays an essential role for in-situ high pressure high temperature studies into the... more Laser heating plays an essential role for in-situ high pressure high temperature studies into the physical and chemical properties of materials in the diamond anvil cell (DAC) and minerals at conditions relevant to the Earth's deep interior. High temperature experiments in the multi-Mbar (over 100 GPa) pressure range require the use of very small samples and consequently the utmost stability
Geophysical Research Letters, 2009
Siderite (FeCO3) forms a complete solid solution with magnesite (MgCO3), the most likely candidat... more Siderite (FeCO3) forms a complete solid solution with magnesite (MgCO3), the most likely candidate for a mantle carbonate. Our experiments with natural siderite reveal spin pairing of d‐orbital electrons of Fe2+ at 43 GPa, as evidenced by a sharp volume collapse of about 10%. The initially colorless crystals assume an intense green color after the transition, which progressively turns to red above 60 GPa. We present clear evidence for the instability of an intermediate spin state in siderite at ambient temperature. At the transition pressure, domains of high and low spin siderite coexist. The unit cell volume difference between magnesite and siderite is significantly decreased by the spin transition, enhancing the solubility between the two calcite‐type minerals. A siderite component in magnesite at lower mantle pressure would significantly increase its density and slightly increase the carbonate bulk modulus.
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Papers by Przemyslaw Dera