MR43C-1515
CO2 Laser Heating System at GSECARS
Laser heating, interfaced with the diamond anvil cell (DAC) pressure generation technique, is a unique tool that allows experimental replication of the conditions of the deep Earth's interior. A unique on-line CO2 (10 micron wavelength) laser heating system has been designed and constructed at GSECARS, Sector 13 of Advanced Photon Source. The system is integrated into the existing fiber laser based setup (1 micron wavelength), and provides several advantages, including being able to directly heat materials that are transparent to near infrared laser light. The technical aspects of the heating system are presented, including the overall design, power control, switch between NIR and CO2 laser heating, sample alignment, temperature measurements, and monitoring of the heating process. X-ray diffraction measurements of silicates in DAC at high pressures and temperatures using the developed setup are presented.
MR43C-1516
Synchrotron x-ray diffraction studies for zincite and ceria under high pressure conditions
Certificated by National Institute of Standards & Technology (NIST), the ZnO and CeO2 powders are intended for use as internal standards for quantitative x-ray diffraction (XRD) analysis, and as external standards for checking the intensity response of x-ray diffraction instruments. For the current high pressure XRD beamlines in synchrotron sources, these oxide powders are normally used as calibration standards at ambient conditions. It is also possible to use these standards as internal standards via their well measured equation of state (EoS). For example, use the wurtzite phase of ZnO to calibrate the wavelength and the distance between sample and detector at ambient conditions. Then use its well-known wurtzite-to-rocksalt type phase transition at 9.3 GPa as fixed point. Its simple rocksalt structure could support such calibrations since we observed its structural stability to high pressure from 10 GPa to at least 215 GPa. A series of synchrotron XRD experimental results will be presented: CeO2 in helium pressure medium up to phase transition pressure; ZnO at high pressure conditions in various pressure media, and the rocksalt phase stability above 200 GPa. High pressure and low temperature down to 15K XRD experiments were also performed for ZnO to fulfill its wurtzite-to-rocksalt type phase transition boundary at low temperature domain. The internal atomic pre-transition distortion effect at low temperature and high pressure will be discussed combine the first-principles calculations results.
MR43C-1517
New Measurements on the Temperature Dependence of Elasticity of Polycrystalline Fe- Wadsleyite and Other Mantle Minerals
Understanding the composition and structure of Earth's mantle requires accurate and precise information about the elastic properties of candidate minerals and how these elastic properties are affected by temperature, pressure, and chemical variations. New elasticity data from room temperature to 640 K at ambient pressure for hot-pressed polycrystalline iron-bearing wadsleyite (Fe:Mg ~ 1:9) will be presented. These data were obtained using resonant ultrasound spectroscopy (RUS) on a Fe-wadsleyite shaped into a right-rectangular parallelepiped with dimensions of 1.965 mm x 1.667 mm x 1.416 mm. From analysis of 42 modal frequencies, the room temperature adiabatic bulk (KS) and shear (G) moduli were found to be 171.3(0.7) GPa and 108.9(0.2) GPa, respectively, with numbers in parentheses indicating uncertainty. These results agree with room temperature values of KS = 170(3) GPa and G = 108(2) GPa found in an earlier study on single-crystal Fe- wadsleyite using Brillouin spectroscopy, and they provide a better anchor point for investigating the temperature dependence of the elasticity of polycrystalline wadsleyite than values of KS = 165.72(0.06) GPa and G = 105.43(0.02) GPa used by previous investigators. We carried out several temperature cycles from room temperature to 500 K (twice) and to 640 K (thrice) in order to determine the elastic properties at elevated temperature and to test reproducibility of the data. The temperature dependence of elastic moduli for Fe-bearing wadsleyite obtained from these experiments will be presented. We will also show recent results of high- temperature elasticity for other polycrystalline mantle minerals (forsterite, garnet).
MR43C-1518
Elasticity of Fayalite and Spinel Polymorph of Fe2SiO4 at High Pressure and Temperature
Fayalite is the iron end-member of the olivine solid solution series. Although there is an extensive set of accurate data about the elastic properties of forsterite, the elasticity data for fayalite end-member is sparse, especially at both high pressure and temperature conditions. In this study, elastic wave velocity measurements on polycrystalline fayalite and its high pressure polymorph spinel at high pressure and temperature were carried out using simultaneous X-ray diffraction, X-ray radiography, and ultrasonic interferometry. The experiment was conducted in a DIA-type cubic anvil apparatus (SAM85) installed at the superwiggler beamline X17B2 in Brookhaven National Laboratory. Ultrasonic data were acquired using a dual mode lithium niobate transducer (10 degree Y-cut, 30 MHz for S wave and 50 MHz for P wave). Boron epoxy cube was used as pressure transmitting medium. The sample was placed in the center of the cube with NaCl and BN as surrounding material. Double polished alumina rod was used as buffer rod. Energy-dispersive X-ray diffraction data for the sample and NaCl were collected for phase identification, density determination, and pressure calculation. Sample length was monitored by X-ray radiographic imaging. Travel time, sample length, and cell parameters were collected along multiple heating/cooling cycles up to 4 GPa and 673 K for fayalite and 7.5 GPa and 1173 K for spinel, from which compressional and shear wave velocities, elastic bulk and shear moduli for both phases can be derived. These results are important in studying the effect of iron on the physical properties of the solid solutions of Mg and Fe end-members at upper mantle and transition zone conditions.
MR43C-1519
Ultrasonic P and S wave Velocity Measurements at Mid-to-Lower Crustal Conditions of Pressure and Temperature in a Piston Cylinder Apparatus
In order to interpret seismic structures in terms of rock type, temperature anomaly, degree of partial melting and distribution of fluids, we have carried out research on the elastic properties of the crustal rocks using ultrasonic measurements. We have developed techniques to perform ultrasonic velocity measurements at mid-to-lower crustal conditions of pressure and temperature. These techniques are now been applied to study the rock physics of exposed deep crustal sections and crustal xenoliths, including gabbro, tonalite, granite, anorthosite, granulite and amphibolite, which were collected from the Tanzawa Mountain of central Japan, Kohistan area of Pakistan, Ichinomegata of NE Japan, Takashima and Kurose of SW Japan, and granulite-facies complex of East Antarctica. Compressional (P) and shear (S) wave velocities for these rock specimens are measured in piston cylinder apparatus. In order to compare directly to seismic velocities at the deep island arc pressures and temperatures, we developed ultrasonic velocity measurements using buffer rod technique. Pt buffer rod is used to isolate the piezoelectric transducer from the high-temperature condition. Travel times through the rock sample were determined with the pulse reflection technique. We are developing a method for simultaneous P-wave and S-wave velocity measurements using dual-mode piezoelectric transducer which generates P-waves and S-waves simultaneously. Using these techniques, we can determine Vp/Vs ratio and Poisson's ratio precisely.
MR43C-1520
The Elastic Properties of Natural Portlandite Ca(OH)2
Portlandite, Ca(OH) 2, is a simple hydroxide with brucite structure (space group P~{3}m1). It is built up of layers of CaO6 octahedra stacked along the c-axis. Portlandite is of basic interest for the cement and concrete research and industries, because it is a major primary solid phase in hydrated portland cement. It is therefore of particular importance to determine the elastic properties of portlandite. So far a computational (Laugesen, 2005) and an experimental (Holuj et al., 1985) study reported the single crystal elastic moduli Cij. However, these results differ significantly in some off-diagonal moduli. We performed Brillouin spectroscopy measurements on natural single crystal portlandite at ambient conditions. Our measurements have been performed in a new Brillouin laboratory set up at the Geoforschungszentrum, Potsdam. The new system features an Eulerian cradle with an inner diameter of 400 mm, and it has been designed to accommodate an internally heated diamond anvil cell to perform Brillouin measurements at high P and T conditions. We have obtained the following values for the elastic moduli (expressed in GPa followed by 1σ uncertainty in parentheses): C11 = 102.0 (2.0), C12 = 32.1 (1.0), C13 = 8.4 (0.4), C14 = 4.5 (0.2), C33 = 33.6 (0.7), C44 = 12.0 (0.3), C66 = (C11-C12)/2 = 35.0 (1.5). With our new measurements we put a better constraint on the value of C13 which is more than 2.5 times larger than reported by Holuj and coworkers, and is closer to the value calculated by Laugesen. A remarkable feature of the elastic behavior is the high elastic anisotropy of portlandite due to its highly anisotropic layered structure. The zero pressure Voigt and Reuss bounds to the adiabatic bulk modulus of portlandite are: K0SV = 37.3 (0.4) GPa and K0SR = 26.0 (0.3) GPa, with a 43% difference between the two bounds. The Voigt and Reuss bounds to the shear modulus are G0V = 24.4 (0.4) GPa and G0R = 17.5 (0.3) GPa, with a 40% difference between the two bounds. The large elastic anisotropy of portlandite is comparable to that of isostructural brucite Mg(OH)2.
MR43C-1521
Brillouin Spectroscopy at the GeoForschungsZentrum-Potsdam: Applications in Geosciences and Materials Science
Knowledge of the elastic properties of earth materials at relevant pressures and temperatures is prerequisite to adequately interpret seismic data and improve our understanding of the composition and mineralogy of the earth's interior. The study of pressure and temperature dependence of acoustic velocity in geo-fluids gives us information about their density with implications for the thermodynamic modelling of diagenetic and metamorphic processes. Furthermore elasticity of synthetic materials is of major interest for several industrial applications. We have recently completed the construction of a new Brillouin System at the GeoForschungsZentrum Potsdam. The new system has been designed to study elasticity of various geological as well as industrial materials at different pressure and temperature conditions. Our Brillouin system consists of a Nd:YVO4 solid state laser operating at a wavelength of 532 nm as light source and a Sandercock-type tandem multipass Fabry-Perot interferometer equipped with a photomultiplier tube for signal detection. Measurements can be performed in 60 or 90 degree symmetric forward scattering or in backscattering geometry. The large positioning system also allows for high temperature measurements in an externally heated diamond anvil cell. We present first results of elasticity measurements both on Earth's materials, such as silicates garnets and oxides, as well as hydroxides and commercially used garnet aluminates, and silicate and borate glasses as proxies for melts. Brillouin scattering has been measured to constrain the density of water-NaCl solutions, for the precise thermodynamic modelling of fluids in metamorphic systems.
MR43C-1522
Phase transitions and equations of state of alkaline earth fluorides CaF2 and SrF2 to 95 GPa
AX2 compounds include a wide range of oxides and salts of broad interest in geoscience, materials science and chemistry, such as SiO2 and CaF2, and have in common a sequence of phase transitions dependent on ionic size ratio and electronic properties (Leger and Haines, 1997). Shock compression studies have shown that CaF2 transforms to a highly incompressible phase above 1 Mbar along the Hugoniot (Nellis, 2007). In this study we examine phase transitions and equations of state of the alkaline earth fluorides CaF2 and SrF2 to 95 GPa. Angle-dispersive x-ray diffraction experiments were performed on CaF2 and SrF2 samples in laser-heated diamond anvil cells at beamlines X17B3 of the National Synchrotron Light Source and 13-ID-D of the GSECARS sector at the Advanced Photon Source. We confirmed that both materials undergo a phase transition from the cubic fluorite structure to the orthorhombic cotunnite-type structure at pressures less than 10 GPa. Both materials further transform to a hexagonal Ni2In-type structure at 84 and 36 GPa, respectively, following laser heating. This finding is consistent with theoretical calculations and the behavior of the analog compound BaF2 (Leger et al., 1995). For SrF2, the Ni2In-type phase was confirmed by Rietveld refinement. On decompression with heating, we found that Ni2In-type SrF2 passes through an intermediate orthorhombic phase at 28 GPa before returning to cotunnite structure at 22 GPa. This transition appears analogous to the isosymmetric phase transition to the Co2Si-type structure reported in PbF2 by Haines et al. (1998). Unit cell parameters and volumes were determined as a function of pressure for the new phases. We also constrained the equation of state of the cotunnite phase of CaF2 to 82 GPa. Fitting the data to a Birch-Murnaghan equation of state yields a zero-pressure bulk modulus of 97.9 GPa with a pressure derivative of 5.6 for cotunnite-type CaF2. This work represents the first synthesis and characterization of the Ni2In-type phase for these compositions and the first report of Co2Si structure in an alkaline earth fluoride.
MR43C-1523
Elasticity of hcp Metals at High Pressure and Temperature: the Quasi-harmonic Case of Cobalt
High-resolution inelastic x-ray scattering (IXS) measurements have been carried out on a single crystal of hcp cobalt at simultaneous high pressure and high temperature. Four out of five independent moduli of the elastic tensor have been derived from simultaneous velocity and density determinations. Our experiments indicate that the elasticity of hcp-Co at high pressure and temperature is well described within the frame of the quasi- harmonic approximation, and that anharmonic high-temperature effects on the elastic moduli, sound velocities and elastic anisotropy are minimal at constant density. These new results on hcp-cobalt are particularly interesting in light of the controversial case of iron, where, on one hand, nuclear resonant inelastic x-ray scattering measurements [1] suggest a negative correlation between the aggregate sound velocities and temperature at constant density, in violation of the "Birch law", and, on the other hand, ab initio finite temperature molecular dynamics simulations [2] support the validity of the "Birch law" for a large number of systems, including bcc- and hcp-Fe. Finally, these measurements highlight the current capabilities of the IXS technique for the studies of elasticity and phonon dispersion of materials under extreme thermodynamic conditions. [1] J.F. Lin et al., Science 308, 1892 (2005). [2] L. Vočadlo, Earth Planet. Sci. Lett. 254, 227 (2007).
MR43C-1524
Structure transition of post-spinels, CaTi2O4, CaMn2O4 and CaFe2O4 under high pressures up to 75GPa
Three structures of CaMn2O4, CaTi2O4 and CaFe2O4 have been proposed as post-spinels phases. Since these structures are very similar, the several arguments or confusions appear in the high-pressure studies, leading many problems that are yet to be solved. Systematic powder diffraction studies related to these three phases were executed under high pressure using synchrotron radiation. Three samples have further high-pressure polymorphs. CaMn2O4 transforms to CaTi2O4 type structure at about 30 GPa. The MnO6 octahedron in the former structure is distorted by the Jahn-Teller effect due to Mn3+ in the octahedral site. This transition probably is induced by the high-low spin transition, because the low spin configuration is very similar to that of Ti3+ in the octahedral site of CaTi2O4. A new phase was observed at pressures over 50 GPa during compression of CaFe2O4. Analysis of this structure was been performed by Monte Carlo method after indexing to find possible structure candidates and then Rietveld profile fitting was applied using the initial models taken from the candidates. This structure, with space group of Pnam, is produced via martensic transformation by displacing atoms in every three layer perpendicular to the c axis. CaTi2O4 also has a new high-pressure polymorph over 39 GPa. The structure has a space group of Bbnm estimated from the indexing. The most provable post-spinel candidate in the mantle is the CaTi2O4 type structure. The CaMn2O4 type structure is only formed at high pressure from spinel phases with atoms susceptible to Jahn
MR43C-1525
Structure Investigation of CaSiO3 Perovskite at 91 GPa
The crystallographic structure of CaSiO3 perovskite at 91(2) GPa is investigated using monochromatic X-ray diffraction and the laser-heated diamond anvil cell with a graphite gasket-insert to increase the volume of the sample under diffraction conditions. We report observations of weak X-ray reflections at d-spaces matching a perovskite super-structure, which appear in addition to splitting of diffraction from the cubic sub-structure. Considering this data in context with the space groups (SGs) of all perovskite structures observed experimentally and recorded in the Inorganic Crystal Structure Database, CaSiO3 perovskite adopts one of two possible tetragonal structures ( P4/ mbm, SG #127, rather than I4/ mcm, SG #123) after cooling from 2000(300) K at this pressure if an orthorhombic or monoclinic unit cell is discounted. When an orthorhombic perovskite structure is considered, reflections from the perovskite super-structure discount Imam (SG #74) and could favor Cmcm (SG #74) above Pbnm (SG #62). The raw diffraction data from CaSiO3 and our analysis are presented in addition to a detailed procedure for the construction of the graphite gasket-insert used during the high pressure experiment. In brief, graphite is machined from a monochromator by electronic discharge and placed within a conventional tungsten gasket. Oriented with its a-axis perpendicular to the direction of force in the diamond anvil cell, a sample chamber is machined within the graphite-insert after indenting with the diamond anvils.
MR43C-1526
Structural Phase Transitions in AuIn2 at High Pressure
The intermetallic compound AuIn2 provides an analog for the high-pressure phases of SiO2, as it is initially in the Fm3m fluorite (CaF2) structure. Synchrotron-based angular-dispersive x-ray diffraction (Advanced Light Source beamline 12.2.2) reveals subtle anomalies in the pressure variation of normalized stress (F) versus Eulerian strain (f) around 3 GPa, coinciding with anomalies observed in fusion, transport and optical data, and potentially associated with the onset of an electronic phase transition. Our diamond-cell experiments (gasketted sample with methanol-ethanol pressure medium) show continuous broadening of diffraction peaks beyond 12 GPa, leading to amorphization near 24 GPa. On further increase of pressure, a crystalline phase appears around 28 GPa and persists upon unloading from 30 GPa to about 5 GPa, then reverting back to the original CaF2 phase. We find the sequence of pressure-induced phase transition documented for CaF2 (fluorite structure Fm3m ¨ PbCl2 Pnma ¨ Ni2In-type P63/mmc and a combination of PbCl2 and Ni2In) to be inadequate in fitting the observed high-pressure diffraction patterns of AuIn2. However, the post-cotunnite structure of PbCl2, BaCl2, BaBr2 and SnCl2 (P1121/c, Z=8) is able to account for most of the prominent peaks in our high-pressure diffraction patterns (a=10.983, b=9.875, c=4.350, Ā=96.6). Many oxides of geophysical interest occur in the CaF2 structure, and study of intermetallic compounds such as AuIn2 may prove useful in suggesting high-pressure metallic phases for these oxides.
MR43C-1527
The High Pressure Synergetic Center at the Advanced Photon Source
Very recently a new group promoting High Pressure (HP) research started at the Advanced Photon Source (APS), the High Pressure Synergetic Center (HPSynC). The HPSynC mission is to establish high-pressure environments at many APS beamlines for the users community. This group will be equivalent to a full beamline team of eight scientists/engineers who, working with HP researchers and beamline scientists, are focusing on the integration of novel high-pressure synchrotron techniques at all specialized beamlines. The HPsynC concept is beyond the normal "extreme environment" infrastructure that is limited to sharing gas-filling equipment, sample preparation laboratory, diamond cells, etc. In addition to these functions, the main role of HPSynC is to facilitate the next level of scientific and technical integration. The HPSynC staff who have the scientific agendas and technical know-how will improve both high-pressure apparati and beamline parameters interactively to optimize the extraordinary capabilities and resource of the synchrotron facility for novel high-pressure experimentation. This new approach is designed to solve the most prominent problem in High Pressure physics using synchrotron radiation. To satisfy the growing demand of beamtime for HP experiments many beamlines have been dedicated to HP research. This allows experienced support of HP experiments, but leaves almost no time for the beamline staff to implement and/or to develop new promissing x-ray techniques to be used at those beamlines. The HP researchers on the other hand are facing the problem of how to actually implement new techniques at these highly sophisticated and specialized beamlines. HPSynC wants to overcome this problem by promoting and developing new techniques together with both groups, the beamline staff and the research team.
MR43C-1528
Heat Capacity of γ-Fe2SiO4 and Thermodynamic Calculation of Fayalite - γ-Fe2SiO4 Phase Transition Boundary
The low-temperature heat capacity (Cp) of γ-Fe2SiO4 was measured between 5 and 303 K using the heat capacity option of a physical properties measurement system (PPMS). Fayalite powder was used as the starting material to synthesize the γ-Fe2SiO4 at 8.5 GPa and 1273 K by a 1,000-ton Walker-type multi-anvil device at the university of Minnesota. The heat capacity data were measured at more than 100 different temperatures with both logarithmic spacing and linear spacing. The measured heat capacity data show a broad lambda-transition at 11.8 K, probably related to a paramagnetic-antiferromagnetic transition just like the 65 K transition in fayalite. The difference in the Cp between fayalite and γ-Fe2SiO4 is reduced as the temperature increases in the range of 50-300 K. The Cp and entropy of γ- Fe2SiO4 at standard temperature and pressure (S°298) are 131.1±0.6 J mol-1K-1 and 140.2±0.4 J mol-1K-1, respectively. The Gibbs free energy at standard pressure and temperature (G°f,298) is calculated to be 1,369.3±2.7 J mol-1 based on the new entropy data. Based on current thermodynamic data, the calculated phase boundary for the fayalite γ- Fe2SiO4 transition at high temperatures and pressures is consistent with the results of previous experimental studies.