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1.
The compressibility of -Mns (alabandite) was determined by x-ray analysis using a Mao-Bell type diamond anvil cell. The zero pressure bulk modulus (K0) is 74±2 GPa with the pressure derivative of the bulk modulus (Ko) fixed at four. Allowing (Ko) to vary yielded a statistically better fit with K0 = 88±6 GPa and k0 = 2.2±0.6. Our data combined with the data of McCammon (1991) gave Ko = 73±1 GPa with ko fixed at four. A fit with ko allowed to vary yielded ko = 75±2 GPa and ko = 3.7±0.4. Alabandite transformed from the B1 structure (NaCl-type) to an unknown high-pressure phase at 26 GPa. The high-pressure phase has lower than hexagonal symmetry and it is stable to at least 46±4 GPa.Also affiliated with the James Franck Institute, University of Chicago  相似文献   

2.
In situ high-pressure synchrotron X-ray diffraction and infrared absorption experiments for gibbsite were performed at room temperature up to 53 and 25 GPa, respectively. A phase transition was confirmed at about 2.5 GPa. The high-pressure phase is indexed as an orthorhombic structure, rather than a triclinic structure as reported in previous studies. The compressibility of gibbsite and its high-pressure polymorph were studied, and their bulk moduli K0 were determined to be 49 and 75 GPa, respectively with K0 as 4. The in situ high-pressure infrared absorption spectra revealed the gradual disordering of hydrogen substructure above 15 GPa in quasihydrostatic compression.  相似文献   

3.
Neutron diffraction data suitable for Rietveld refinements were collected on a powder sample of synthetic Mg(OH)2 by the Polaris time-of-flight spectrometer (ISIS spallation source, U.K.) at 10-4 7.8(3) and 10.9(6) GPa. The Paris-Edinburgh high-pressure cell with WC anvils was used. Pressure calibration and equation-ofstate results were attained by separate runs with an NaCl internal standard. Interpolation of p(V) data by the fourth-order Birch-Murnaghan e.o.s. yields K 0=41(2) GPa, K0=4(2) and K0=1.1(9) GPa-1. The bulk modulus obtained is smaller than previously reported results. Rietveld refinements (R prof =1.45% and 2.02% at 10-4 and 10.9 GPa) show that H lies on the threefold axis (1/3, 2/3, z) up to 10.9 GPa, where a model with H disordered in (x, 2x, z) can be refined. In the latter case, a hydrogen bond with O-H=0.902(7), H..O=2.026(8) Å and <>=145.9 (7)° is observed. Differences with previous results for deuterated brucite are discussed. The onset of H disorder, and a jump of the c/a ratio vs. pressure at 6–7 GPa, may be related to a second-order phase transition consistent with recently reported Raman spectroscopic results.  相似文献   

4.
A single-crystal of composition CaNiSi2O6 (space group C2/c) was investigated at high pressure up to about 7.8 GPa by X-ray diffraction. The unit-cell parameters were measured at 18 different pressures. The P-V data were fitted by a third-order Birch-Murnaghan equation of state V0=435.21(1) Å3, K 0=117.6(3) GPa and K=6.4(1). The linear axial compressibilities a, b, c and a sin are 2.14(1), 3.00(1), 2.43(1) and 1.63(1) × 10–3 GPa–1. Comparing the compressibility data with other CaM1Si2O6 pyroxenes we suggest that the empirical K × V = constant relationships are followed in C2/c pyroxenes only if the same valence electron character is shared.  相似文献   

5.
In-situ synchrotron X-ray diffraction (XRD) experiments of a natural apatite with the formula of Ca5(PO4)3F0.94Cl0.06 were carried out using a diamond anvil cell and angle-dispersive technique at Photon Factory (PF), Japan. Pressure–volume data were collected up to 7.12 GPa at 300 K. The pressures were determined from the ruby fluorescence spectra shift. The unit-cell parameters and volume decreased systematically with increasing pressure, and a reliable isothermal bulk modulus and its pressure derivative were obtained in this study. The third-order Birch–Murnaghan equation of state yielded the isothermal bulk modulus of KT=91.5(38) GPa, its pressure derivative KT= 4.0(11), and the zero-pressure volume V0=524.2(3) Å3.  相似文献   

6.
Polycrystalline samples of natural edingtonite (New Brunswick, Canada) and thomsonite (Oregon, USA) were studied up to 6 GPa using monochromatic synchrotron X-ray powder diffraction and a diamond-anvil cell with a methanol:ethanol:water mixture as a penetrating pressure-transmitting fluid. Unlike natrolite, previously studied under the same conditions, edingtonite and thomsonite do not show any apparent pressure-induced hydration (PIH) or phase transitions. All these fibrous zeolites are characterized by their anisotropic compressibilities, with the linear compressibilities of the fibrous chains (c-axis) being as small as one third of those perpendicular to the chains (a-, b-axes); for edingtonite, 0 a =0.0050(3) GPa–1, 0 b =0.0054(2) GPa–1, 0 c =0.0034(1) GPa–1; for thomsonite, 0 a = 0.0080(2) GPa–1, 0 b =0.0084(2) GPa–1, 0 c =0.0032(1) GPa–1. The pressure–volume data were fitted to a second-order Birch–Murnaghan equation of state using a fixed pressure derivative of 4. As a result of the 0000-type connectivity of the chains, the bulk modulus of edingtonite is found to be about 40% larger than that of thomsonite; KEDI 0=73(3) GPa, KTHO 0=52(1) GPa. Distance least-squares refinements were used to model the expected framework, following the observed linear compression behaviors. The chain-bridging T–O–T angle is proposed to be correlated with the different compressibilities across the chains in each framework type.  相似文献   

7.
In-situ synchrotron X-ray diffraction experiments were conducted using the SPEED-1500 multi-anvil press of SPring-8 on stishovite SiO2 and pressure-volume-temperature data were collected at up to 22.5 GPa and 1,073 K, which corresponds to the pressure conditions of the base of the mantle transition zone. The analysis of room-temperature data yielded V0=46.56(1) Å3, KT 0=296(5) GPa and K T =4.2(4), and these properties were consistent with the subsequent thermal equation of state (EOS) analyses. A fit of the present data to high-temperature Birch-Murnaghan EOS yielded (KT /T) P =–0.046(5) GPa K–1 and = a + bT with values of a =1.26(11)×10–5 K–1 and b =1.29(17)×10–8 K–2. A fit to the thermal pressure EOS gives 0=1.62(9)×10–5 K–1, ( K T / T) V =–0.027(4) GPa K–1 and (2P /T 2) V =27(5)×10–7 GPa K–2. The lattice dynamical approach by Mie-Grüneisen-Debye EOS yielded 0=1.33(6), q =6.1(8) and 0=1160(120) K. The strong volume dependence of the thermal pressure of stishovite was revealed by the analysis of present data, which was not detectable by the previous high-temperature data at lower pressures, and this yields ( K T / T) V 0 and q 1. The analyses for the fictive volume for a and c axes show that relative stiffness of c axis to a axis is similar both on compression and thermal expansion. Present EOS enables the accurate estimate of density of SiO2 in the deep mantle conditions.  相似文献   

8.
The bulk modulus, K 0, and its pressure derivative K0, of -(Mg0.6, Fe0.4)2SiO4 have been accurately determined to 50.0 GPa under hydrostatic conditions at room temperature in a diamond cell using synchrotron radiation. Our results agree with Brillouin and ultrasonic measurements on -Mg2SiO4 at low pressure, indicating normal elastic behaviour in the metastable pressure range of this high pressure mineral. Our values of K 0 and k0 are 183.0 GPa and 5.4, respectively.  相似文献   

9.
New internally consistent interpretations of the phases represented by the high pressure phase shock wave data for an albite-rich rock, Jadeite, and nepheline in the system NaAlSiO4-SiO2, are obtained using the results of static high pressure investigations, and the recent discovery of the hollandite phase in a shocked meteorite. We conclude that nepheline transforms directly to the calcium ferrite structure, whereas albite transforms possibly to the hollandite structure. Shock Hugoniots for the other plagioclase and alkali feldspars also indicate that these transform to hollandite structures. The pressure-volume data at high pressure could alternatively represent the compression of an amorphous phase. Moreover, the shock Hugoniot data are expected to reflect the properties of the melt above shock stresses of 60–80 GPa. The third order Birch-Murnaghan equation of state parameters are: Kos=275±38 GPa and Kos=1.6±1.5 for the calcium ferrite type NaAlSiO4, Kos=186±33 GPA and Kos=2.6±1.7 for the albite-rich hollandite, Kos=236±45 GPa and Kos=2.3±2.0 for the orthoclase-rich hollandite, and Kos=190 to 210 GPa and Kos2.2 for the anorthite-rich hollandite.  相似文献   

10.
High-pressure single-crystal X-ray diffraction measurements of lattice parameters of the compound Li2VOSiO4, which crystallises with a natisite-type structure, has been carried out to a pressure of 8.54(5) GPa at room temperature. Unit-cell volume data were fitted with a second-order Birch-Murnaghan EoS (BM-EoS), simultaneously refining V 0 and K 0 using the data weighted by the uncertainties in V. The bulk modulus is K 0 = 99(1) GPa, with K′ fixed to 4. Refinements of third order equations-of-state yielded values of K′ that did not differ significantly from 4. The compressibility of the unit-cell is strongly anisotropic with the c axis (K 0(c) = 49.7 ± 0.5 GPa) approximately four times more compressible than the a axis (K 0(a) = 195 ± 3 GPa).  相似文献   

11.
Brackets on the melting temperature of K2CO3 were experimentally determined at 1.86 ± 0.02 GPa (1,163–1,167°C), 2.79 ± 0.03 GPa (1,187–1,195°C), and 3.16 ± 0.04 GPa (1,183–1,189°C) in a piston-cylinder apparatus. These new data, in combination with published experiments at low pressure (<0.5 GPa), establish the K2CO3 fusion curve to 3.2 GPa. On the basis of these experiments and published thermodynamic data for crystalline and liquid K2CO3, the high-pressure density and compressibility of K2CO3 liquid were derived from the fusion curve. The pressure dependence of the liquid compressibility (K′0 = dK 0/dP, where K 0 = 1/β0) is between 16.2 and 11.6, with a best estimate of 13.7, in a third-order Birch–Murnaghan equation of state (EOS). This liquid K′0 leads to a density of 2,175 ± 36 kg/m3 at 4 GPa and 1,500°C, which is ∼30% lower than that reported in the literature on the basis of the falling-sphere method at the same conditions. The uncertainty in the liquid K′0 leads to an error in melt density of ± 2% at 4 GPa; the error decreases with decreasing pressure. With a K′0 of 13.7, the compressibility of K2CO3 at 1,500°C and 1 bar (K 0 = 3.8 GPa) drops rapidly with increasing pressure ( ), which prevents a density crossover with silicate melts, such as CaAlSi2O8 and CaMgSi2O6, at upper mantle depths.  相似文献   

12.
Four crystals of synthetic wadsleyite, -(Mg,Fe)2SiO4, were mounted together in one diamond-anvil cell for the determination of unit-cell parameters as a function of pressure. The Fe/(Fe+Mg) are 0.00, 0.08, 0.16, and 0.25 (the most iron-rich stable composition). Unit-cell refinements were made at 12 pressures up to 4.5 GPa. No phase transitions were observed and all crystals remained dimensionally orthorhombic. Of the three axes, c is the most compressible (0.000239(3) GPa-1), whereas compressibilities of a and b are both about 30% less. The Fe content has no systematic effect on volume or linear compressibilities. Bulk moduli, based on a Birch-Murnaghan equation of state (K assumed to be 4.00) are 160(3), 169(3), 164(2), and 165(3) GPa for the four crystals in order of increasing Fe. Substitution of Fe for Mg, therefore, does not appear to have a systematic effect on bulk modulus. Other factors, especially Fe3+/Fe2+ and other deviations from the strict Mg2SiO4-Fe2SiO4 binary, may have a greater influence on compressibility.  相似文献   

13.
High-pressure and high-temperature experiments conducted in a laser-heated diamond-anvil cell with a synchrotron X-ray diffraction method have revealed a phase transformation in the aragonite-type SrCO3 at pressures above 10 GPa. The new phase has an orthorhombic symmetry and was confirmed to remain stable to 32 GPa. The Birch-Murnaghan equation of state for new phase was determined from the experimental unit cell parameters, with K0 = 101 (± 16) GPa, K0 = 4 (constrained value), and V0 = 111.9 (± 2.2). This transformation in SrCO3 is different from that in BaCO3 as reported in previous studies. After decompression at ambient pressure, the high-pressure phase transforms to a metastable structure, which has an orthorhombic symmetry. This result should also resolve a dispute regarding the stable high-pressure phases in BaCO3, which is an analog material of CaCO3 and SrCO3.This revised version was published in February 2005 with corrections to the Introduction and to the References.  相似文献   

14.
A high-pressure single-crystal x-ray diffraction study of perovskite-type MgSiO3 has been completed to 12.6 GPa. The compressibility of MgSiO3 perovskite is anisotropic with b approximately 23% less compressible than a or c which have similar compressibilities. The observed unit cell compression gives a bulk modulus of 254 GPa using a Birch-Murnaghan equation of state with K set equal to 4 and V/V 0 at room pressure equal to one. Between room pressure and 5 GPa, the primary response of the structure to pressure is compression of the Mg-O and Si-O bonds. Above 5 GPa, the SiO6 octahedra tilt, particularly in the [bc]-plane. The distortion of the MgO12 site increases under compression. The variation of the O(2)-O(2)-O(2) angles and bondlength distortion of the MgO12 site with pressure in MgSiO3 perovskite follow trends observed in GdFeO3type perovskites with increasing distortion. Such trends might be useful for predicting distortions in GdFeO3-type perovskites as a function of pressure.  相似文献   

15.
The effect of (Mg,Fe) substitution on the compression and pressure-induced amorphization of olivines has been investigated up to more than 50 GPa in a diamond anvil cell through energy-dispersive X-ray diffraction experiments with synchrotron radiation. For the four (Mg1–x , Fe x )2SiO4 olivines studied, the compressibility is the highest along the b axis and the smallest along the a axis. For compositions with x = 0, 0.17, 0.66, and 1, the slope of the volume-pressure curves shows a rapid decrease at pressures of around 42, 34, 20 and 10 GPa, respectively. Assuming K0 = 4, we obtained at lower pressures with a Birch-Murnaghan equation of state essentially the same room-pressure bulk modulus for all olivines, namely K 0 = 131 ± 6 GPa, in agreement with previous single-crystal compression and ultrasonic measurements. At higher pressures, the compression becomes nearly isotropic and the materials very stiff. These changes could precede partial transformation of olivines to a high-pressure polymorph related to the spinel structure. Only a small fraction of olivines seems to transform actually to this phase, however, because most of the material undergoes instead pressure-induced amorphization which take place at considerably higher pressures for Mg-than for Fe-rich olivines.  相似文献   

16.
The stability and pressure–volume equation of state of iron–silicon alloys, Fe-8.7 wt% Si and Fe-17.8 wt% Si, have been investigated using diamond-anvil cell techniques up to 196 and 124 GPa, respectively. Angular–dispersive X-ray diffractions of iron–silicon alloys were measured at room temperature using monochromatic synchrotron radiation and an imaging plate (IP). A bcc–Fe-8.7 wt% Si transformed to hcp structure at around 1636 GPa. The high-pressure phase of Fe-8.7 wt% Si with hexagonal close-packed (hcp) structure was found to be stable up to 196 GPa and no phase transition of bcc–Fe-17.8 wt% Si was observed up to 124 GPa. The pressure–volume data were fitted to a third-order Birch–Murnaghan equation of state (BM EOS) with zero–pressure parameters: V0=22.2(8) Å3, K0=198(9) GPa, and K0=4.7(3) for hcp–Fe-8.7 wt% Si and V0=179.41(45) Å3, K0=207(15) GPa and K0=5.1(6) for Fe-17.8 wt% Si. The density and bulk sound velocity of hcp–Fe-8.7 wt% Si indicate that the inner core could contain 3–5 wt% Si.  相似文献   

17.
The elastic moduli of single crystals of pyrope-rich garnet and San Carlos olivine have been measured over a 3 GPa pressure range at room temperature. The combination of improved ultrasonic techniques and this large pressure range provide for more reliable characterization of the pressure dependence of acoustic wave velocities than has previously been possible. First and second pressure derivatives of the velocities have been determined within 1 percent and 10 percent respectively. The Hashin-Shtrikman bounds for the pressure dependences of the bulk and shear moduli of the garnet used in this study are; K = 173.6 GPa, K = 4.93, K = –0.28 GPa–1, G= 94.9 GPa, G = 1.56, G = –0.08 GPa–1 and the Hashin-Shtrikman least-upper bounds and greatestlower bounds for the pressure dependences of the bulk and shear moduli of the San Carlos olivine are K=129.8 GPa, K = 4.66, K= –0.15 GPa–1, G = 77.8 GPa, G = 1.93, G = –0.11 GPa–1 and K = 129.2 GPa, K = 4.63, K= –0.15 GPa–1 G = 77.3 GPa, G=1.96, G = –0.11 GPa–1 respectively. The determination of the room-pressure elastic moduli of this pyrope-almandine garnet removes the previously observed anomaly in the predictions of systematic treatments of variations of the elastic moduli of garnets with composition. The determination of the second pressure derivatives of the moduli of garnet and olivine illustrates the importance of these terms in extrapolations to higher pressures — with K/P for these crystals being reduced by 17 percent and 9 percent respectively over the 3 GPa pressure range.  相似文献   

18.
The high-pressure behaviour of millerite NiS up to 34.7 GPa was studied using single-crystal X-ray diffraction techniques. Under ambient pressure, 8.3, 19.2 and 26.8 GPa crystal-structure determinations were performed. No phase transition was observed and the fit of the Birch-Murnaghan equation of state gave a bulk modulus K=111(1) GPa and a pressure derivative K=5.0(1) at high pressure and room temperature. The high-temperature modification of NiS belongs to the NiAs type and has the smaller volume per formula unit. High-pressure–high-temperature X-ray diffraction studies on NiS powder indicate that the transition temperature is strongly dependent on pressure. Owing to the higher compressibility of millerite compared with that of the high-temperature phase, it is assumed that the NiAs-type is not the stable phase at high pressures.  相似文献   

19.
New high-pressure orthorhombic (GdFeO3-type) perovskite polymorphs of MnSnO3 and FeTiO3 have been observed using in situ powder X-ray diffraction in a diamond-anvil cell with synchrotron radiation. The materials are produced by the compression of the lithium niobate polymorphs of MnSnO3 and FeTiO3 at room temperature. The lithium niobate to perovskite transition occurs reversibly at 7 GPa in MnSnO3, with a volume change of -1.5%, and at 16 GPa in FeTiO3, with a volume change of -2.8%. Both transitions show hysteresis at room temperature. For MnSnO3 perovskite at 7.35 (8) GPa, the orthorhombic cell parameters are a=5.301 (2) A, b=5.445 (2) Å, c=7.690 (8) Å and V= 221.99 (15) Å3. Volume compression data were collected between 7 and 20 GPa. The bulk modulus calculated from the compression data is 257 (18) GPa in this pressure region. For FeTiO3 perovskite at 18.0 (5) GPa, cell parameters are a=5.022 (6) Å, b=5.169 (5) Å, c=7.239 (9) Å and V= 187.94 (36) Å3. Based on published data on the quench phases, the FeTiO3 perovskite breaks down to a rocksalt + baddelyite mixture of FeO and TiO2 at 23 GPa. This is the first experimental verification of the pressure-induced breakdown of a perovskite to simple oxides.  相似文献   

20.
The high-pressure behaviour of a synthetic P21/c ferrian magnesian spodumene, M2 (Li0.85Mg0.09Fe2+ 0.06)M1(Fe3+ 0.85Mg0.15)Si2O6, has been investigated using in situ single-crystal X-ray diffraction and Raman spectroscopy. No phase transition has been observed within the pressure range investigated. The isothermal equation of state up to 7 GPa was determined. V0, KT0 and K, simultaneously refined with a Murnaghan equation of state, are: V0= 415.66(7) Å3, KT0=83(1) GPa and K=9.6(6). The magnitudes of the principal unit-strain coefficients were calculated and their ratios 1:2:3=1.00:1.85:2.81 at P=6.83 GPa indicate a very strong anisotropy. Monitoring of the intensity of b-type reflections (h+k= 2n+1) confirms that from room conditions up to 7 GPa the primitive lattice is maintained. Raman spectra have been collected up to 7.4 GPa. No change in the number of observed vibrational modes occurs in the pressure range investigated. At high frequency, the Raman doublet relative to the Si–O–Si vibrations of the two distinct tetrahedral chains is a broad band at room pressure, however, the frequency difference between the two modes increases with increasing pressure.Operating system: Windows NT  相似文献   

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