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1.
This is an exploratory study on the high-pressure (HP) structural evolution of a zeolitic framework (with LEV topology) on the basis of geometric modelling and previously published accurate unit-cell constants measured by means of single-crystal X-ray diffraction. The geometric simulations for 11 P values from 0 to 5 GPa gives more insight into the HP-behaviour of levyne, showing that the anomalous elastic behaviour of this zeolite observed under hydrostatic conditions at low P (P<1 GPa) is due to a double change in the compressional mechanism. Since the geometric simulation is not restricted to using the experimentally determined cell parameters, simulations of uniaxial compression along the [001] direction and of compression in the (001) plane have been performed, shedding more light on the compression mechanisms under non-hydrostatic regimes, which are difficult to access experimentally. The mechanisms associated with compressions along different axes provide insight into the hydrostatic compression mechanisms leading to the anomalous elastic behaviour.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.  相似文献   

2.
We report a comparative study on the high pressure (HP) structural behaviour of a fibrous zeolite (with EDI topology) on the basis of rigid unit modes (RUM) modelling and previously published single-crystal X-ray diffraction. HP single-crystal diffraction data lead to a more precise determination of the elastic parameters (axial and volume compressibilities) useful to define the equation-of-state under isothermal conditions, and the structural refinements are useful to describe the main deformation mechanisms of the Si/Al framework and extra-framework content at high pressure. The RUM modelling is applied to simulate the compressive behaviour of the framework, under hydrostatic and non-hydrostatic conditions, using a minimum number of parameters, and to describe the deformation mechanism intuitively in terms of the rotations of the SiO4 polyhedra. The local and global P-induced deformation mechanisms of the Si/Al framework observed in experiment (channel ellipticity, SBU rotation) are well reproduced by RUM modelling. The simulation of uniaxial compression (non-hydrostatic conditions) shows an interesting result on the structural behaviour. This comparative study tests the reliability of the RUM modelling in open-framework silicates with a complicated crystal structure.Electronic Supplementary Material: Supplementary material to this paper is available in electronic form at  相似文献   

3.
The melting temperature of Fe–18 wt% Si alloy was determined up to 119 GPa based on a change of laser heating efficiency and the texture of the recovered samples in the laser-heated diamond anvil cell experiments. We have also investigated the subsolidus phase relations of Fe–18 wt% Si alloy by the in-situ X-ray diffraction method and confirmed that the bcc phase is stable at least up to 57 GPa and high temperature. The melting curve of the alloy was fitted by the Simon’s equation, P(GPa)/a = (T m(K)/T 0) c , with parameters, T 0 = 1,473 K, a = 3.5 ± 1.1 GPa, and c = 4.5 ± 0.4. The melting temperature of bcc Fe–18 wt% Si alloy is comparable with that of pure iron in the pressure range of this work. The melting temperature of Fe–18 wt% Si alloy is estimated to be 3,300–3,500 K at 135 GPa, and 4,000–4,200 K at around 330 GPa, which may provide the lower bound of the temperatures at the core–mantle boundary and the inner core–outer core boundary if the light element in the core is silicon.  相似文献   

4.
A compressional study of (Na,Ca)(Ti3+,Mg)Si2O6-clinopyroxenes was carried out at high pressures between 10−4 and 10.2 GPa using in situ single-crystal X-ray diffraction, Raman spectroscopy and optical absorption spectroscopy. Compressional discontinuities accompanied by structural changes, in particular, the appearance of two distinct Ti3+–Ti3+ distances within the octahedral chains at 4.37 GPa, provide evidence for the occurrence of a phase transition in NaTi3+Si2O6. Equation-of-state parameters are K 0 = 115.9(7) GPa with K′ = −0.9(3) and K 0 = 102.7(8) GPa with K′ = 4.08(5) for the low- and high-pressure range, respectively. The transition involves a C2/c–P [`1] \overline{1} symmetry change, which can be confirmed by the occurrence of new modes in Raman spectra. Since no significant discontinuity in the evolution of the unit-cell volume with pressure has been observed, the transition appears to be second-order in character. The influence of the coupled substitution Na+Ti3+↔Ca2+Mg2+ on the static compression behavior and the structural stability has been investigated using a sample of the intermediate composition (Na0.54Ca0.46)(Mg0.46Ti0.54)Si2O6. No evidence for a deviation from continuous compression behavior has been found, neither in lattice parameter nor in structural data and the fit of a third-order Birch–Murnaghan equation-of-state to the pressure–volume data yields a bulk modulus of K 0 = 109.1(5) GPa and K′ = 5.02(13). Raman and polarized absorption spectra have been compared to NaTiSi2O6 and reveal major similarities. The main driving force for the phase transition in NaTi3+Si2O6 is the localization of the Ti3+ d-electron and the accompanying distortion, which is suppressed in the (Na,Ca)(Ti3+,Mg)Si2O6-clinopyroxene.  相似文献   

5.
We present isothermal volume compression behavior of two polycrystalline (Mg,Fe)O samples with FeO = 39 and 78 mol% up to ~90 GPa at 300 K using synchrotron X-ray diffraction and neon as a pressure-transmitting medium. For the iron-rich (Mg0.22Fe0.78)O sample, a structural transition from the B1 structure to a rhombohedral structure was observed at 41.6 GPa, with no further indication of changes in structural or compression behavior changes up to 93 GPa. In contrast, a change in the compression behavior of (Mg0.61Fe0.39)O was observed during compression at P ≥ 71 GPa and is indicative of a spin crossover occurring in the Fe2+ component of (Mg0.61Fe0.39)O. The low-spin state exhibited a volume collapse of ~3.5%, which is a larger value than what was observed for a similar composition in a laser-heated NaCl medium. Upon decompression, the volume of the high-spin state was recovered at approximately 65 GPa. We therefore bracket the spin crossover at 65 ≤ P (GPa) ≤ 77 at 300 K (Mg0.61Fe0.39)O. We observed no deviation from the B1 structure in (Mg0.61Fe0.39)O throughout the pressure range investigated.  相似文献   

6.
 The structural behavior of synthetic gahnite (ZnAl2O4) has been investigated by X-ray powder diffraction at high pressure (0–43 GPa) and room temperature, on the ID9 beamline at ESRF. The equation of state of gahnite has been derived using the models of Birch–Murnaghan, Vinet and Poirier–Tarantola, and the results have been mutually compared (the elastic bulk modulus and its derivatives versus P determined by the third-order Birch–Murnaghan equation of state are K 0=201.7(±0.9) GPa, K ′ 0=7.62(±0.09) and K ″ 0=−0.1022 GPa−1 (implied value). The compressibilities of the tetrahedral and octahedral bond lengths [0.00188(8) and 0.00142(5) GPa−1 at P=0, respectively], and the␣polyhedral volume compressibilities of the four-␣and␣sixfold coordination sites [0.0057(2) and 0.0041(2) GPa−1 at P=0, respectively] are discussed. Received: 15 January 2001 / Accepted: 23 April 2001  相似文献   

7.
The stability of hercynite (FeAl2O4) has been investigated experimentally between 7 and 24 GPa and 900 and 1,700°C. Hercynite breaks down to its constituent oxides at 7–8.5 GPa and temperatures >1,000°C. The incorporation of a small magnetite component in the hercynite necessitated a small correction to fix the location of the endmember reaction: FeAl2O4  = Al2O3 + FeO in P–T space. After making this correction, the position of the phase boundary was used to evaluate thermodynamic data for hercynite. Our results support a relatively large S 298° for hercynite, on the order of 115 J mol−1 K−1. Experiments up to 24 GPa and 1,400°C failed to detect any high-pressure polymorph of FeAl2O4; only corundum + wüstite were detected. This behaviour contrasts with that observed for the analogous MgAl2O4 system where the constituent oxides recombine at high pressure to produce “post-spinel” phases with CaFe2O4-type and CaTi2O4-type structures.  相似文献   

8.
 The second-order elastic constants of CaF2 (fluorite) have been determined by Brillouin scattering to 9.3 GPa at 300 K. Acoustic velocities have been measured in the (111) plane and inverted to simultaneously obtain the elastic constants and the orientation of the crystal. A notable feature of the present inversion is that only the density at ambient condition was used in the inversion. We obtain high-pressure densities directly from Brillouin data by conversion to isothermal conditions and iterative integration of the compression curve. The pressure derivative of the isentropic bulk modulus and of the shear modulus determined in this study are 4.78 ± 0.13 and 1.08 ± 0.07, which differ from previous low-pressure ultrasonic elasticity measurements. The pressure derivative of the isothermal bulk modulus is 4.83 ± 0.13, 8% lower than the value from static compression, and its uncertainty is lower by a factor of 3. The elastic constants of fluorite increase almost linearly with pressure over the whole investigated pressure range. However, at P ≥ 9 GPa, C 11 and C 12 show a subtle structure in their pressure dependence while C 44 does not. The behavior of the elastic constants of fluorite in the 9–9.3 GPa pressure range is probably affected by the onset of a high-pressure structural transition to a lower symmetry phase (α-PbCl2 type). A single-crystal Raman scattering experiment performed in parallel to the Brillouin measurements shows the appearance of new features at 8.7 GPa. The new features are continuously observed to 49.2 GPa, confirming that the orthorhombic high-pressure phase is stable along the whole investigated pressure range, in agreement with a previous X-ray diffraction study of CaF2 to 45 GPa. The high-pressure elasticity data in combination with room-pressure values from previous studies allowed us to determine an independent room-temperature compression curve of fluorite. The new compression curve yields a maximum discrepancy of 0.05 GPa at 9.5 GPa with respect to that derived from static compression by Angel (1993). This comparison suggests that the accuracy of the fluorite pressure scale is better than 1% over the 0–9 GPa pressure range. Received: 10 July 2001 / Accepted: 7 March 2002  相似文献   

9.
A single crystal X-ray diffraction study on lithium tetraborate Li2B4O7 (diomignite, space group I41 cd) has been performed under pressure up to 8.3 GPa. No phase transitions were found in the pressure range investigated, and hence the pressure evolution of the unit-cell volume of the I41 cd structure has been described using a third-order Birch–Murnaghan equation of state (BM-EoS) with the following parameters: V 0  = 923.21(6) Å3, K 0  = 45.6(6) GPa, and K′ = 7.3(3). A linearized BM-EoS was fitted to the axial compressibilities resulting in the following parameters a 0  = 9.4747(3) Å, K 0a  = 73.3(9) GPa, K′ a  = 5.1(3) and c 0  = 10.2838(4) Å, K 0c  = 24.6(3) GPa, K′ c  = 7.5(2) for the a and c axes, respectively. The elastic anisotropy of Li2B4O7 is very large with the zero-pressure compressibility ratio β 0c /β 0a  = 3.0(1). The large elastic anisotropy is consistent with the crystal structure: A three-dimensional arrangement of relatively rigid tetraborate groups [B4O7]2− forms channels occupied by lithium along the polar c–axis, and hence compression along the c axis requires the shrinkage of the lithium channels, whereas compression in the a direction depends mainly on the contraction of the most rigid [B4O7]2− units. Finally, the isothermal bulk modulus obtained in this work is in general agreement with that derived from ultrasonic (Adachi et al. in Proceedings-IEEE Ultrasonic Symposium, 228–232, 1985; Shorrocks et al. in Proceedings-IEEE Ultrasonic Symposium, 337–340, 1981) and Brillouin scattering measurements (Takagi et al. in Ferroelectrics, 137:337–342, 1992).  相似文献   

10.
The elastic behaviour and the high-pressure structural evolution of a natural topaz, Al2.00Si1.05O4.00(OH0.26F1.75), have been investigated by means of in situ single-crystal X-ray diffraction up to 10.55(5) GPa. No phase transition has been observed within the pressure range investigated. Unit-cell volume data were fitted with a third-order Birch-Murnaghan Equation of State (III-BM-EoS). The III-BM-EoS parameters, simultaneously refined using the data weighted by the uncertainties in P and V, are: V 0=345.57(7) Å3, K T0=164(2) GPa and K′=2.9(4). The axial-EoS parameters are: a 0=4.6634(3) Å, K T0(a)=152(2) GPa, K′(a)=2.8(4) for the a-axis; b 0=8.8349(5) Å, K T0(b)=224(3) GPa, K′(b)=2.6(6) for the b-axis; c 0=8.3875(7) Å, K T0(c)=137(2) GPa, K′(c)=2.9(4) for the c-axis. The magnitude and the orientation of the principal Lagrangian unit-strain ellipsoid were determined. At P−P 0=10.55 GPa, the ratios ε1:ε2:ε3 are 1.00:1.42:1.56 (with ε1||b, ε2||a, ε3||c and |ε3| > |ε2| > |ε1|). Four structural refinements, performed at 0.0001, 3.14(5), 5.79(5) and 8.39(5) GPa describe the structural evolution in terms of polyhedral distortions.  相似文献   

11.
Stress-induced proton disorder in hydrous ringwoodite   总被引：1，自引：1，他引：0  
We have measured in situ high-pressure IR absorption of synthetic hydrous (MgxFe1−x)2SiO4 ringwoodites (x = 0.00 to 0.61) up to a maximum pressure of 30 GPa. In our study, we combined the megabar-type diamond-anvil cell (DAC) with conventional and synchrotron FTIR spectroscopy. The high-pressure measurements were performed in three different pressure-transmitting environments: (1) CsI powder, (2) cryogenically loaded liquid argon, and (3) cryogenically loaded liquid argon annealed at 8.6 GPa at temperature of 120°C before further pressure increase. Between 10 and 12 GPa, all the samples loaded with methods (1) and (2), independent on composition, showed a sudden disappearance of the prominent OH-stretching feature and simultaneous discontinuities and/or changes in the pressure dependence of lattice vibrations compared with spectra of samples loaded with method (3). In experiments performed with method (3) the OH-stretching vibrations as well as lattice vibrations could be observed up to 30 GPa and their pressure behavior (dν/dP) can well be described by linear fits. Molecular vibrations, such as the OH stretching, are sensitive to non-hydrostatic conditions, especially in minerals with highly symmetric structures. We interpret the disappearance of the OH bands using methods (1) and (2) as a stress-induced proton disordering in hydrous ringwoodite. Our results confirm that argon pressure medium produces strongly non-hydrostatic conditions comparable to CsI or KBr, if it is not thermally annealed at pressures above 8 GPa. Our results suggest that the transition observed in hydrous Mg-ringwoodite end member is not present in compositions containing Fe. By comparing the behavior of samples compressed in different environments, we suggest that sudden disappearance of the OH-stretching band in hydrous ringwoodite could be driven by deterioration of the quasi-hydrostatic stress condition instead of a pressure-induced effect.  相似文献   

12.
The high-pressure elastic behaviour of a synthetic zeolite mordenite, Na6Al6.02Si42.02O96·19H2O [a=18.131(2), b=20.507(2), c=7.5221(5) Å, space group Cmc21], has been investigated by means of in situ synchrotron X-ray powder diffraction up to 5.68 GPa. No phase transition has been observed within the pressure range investigated. Axial and volume bulk moduli have been calculated using a truncated second-order Birch–Murnaghan equation-of-state (II-BM-EoS). The refined elastic parameters are: V 0=2801(11) Å3, K T0= 41(2) GPa for the unit-cell volume; a 0=18.138(32) Å, K T0(a)=70(8) GPa for the a-axis; b 0=20.517(35) Å, K T0(b)=29(2) GPa for the b-axis and c 0=7.531(5) Å, K T0(c)=38(1) GPa for the c-axis [K T0(a): K T0(b): K T0(c)=2.41:1.00:1.31]. Axial and volume Eulerian finite strain versus “normalized stress” plots (fe–Fe plot) show an almost linear trend and the weighted linear regression through the data points yields the following intercept values: Fe(0)=39(4) GPa for V; Fe a (0)=65(18) GPa for a; Fe b (0)=28(3) GPa for b; Fe c (0)=38(2) GPa for c. The magnitudes of the principal Lagrangian unit-strain coefficients, between 0.47 GPa (the lowest HP-data point) and each measured P>0.47 GPa, were calculated. The unit-strain ellipsoid is oriented with ε1 || b, ε2 || c, ε3 || a and |ε1|> |ε2|> |ε3|. Between 0.47 and 5.68 GPa the relationship between the unit-strain coefficient is ε1: ε2: ε3=2.16:1.81:1.00. The reasons of the elastic anisotropy are discussed.An erratum to this article can be found at  相似文献   

13.
The thermoelastic behavior of a natural clintonite-1M [with composition: Ca1.01(Mg2.29Al0.59Fe0.12)Σ3.00(Si1.20Al2.80)Σ4.00O10(OH)2] has been investigated up to 10 GPa (at room temperature) and up to 960°C (at room pressure) by means of in situ synchrotron single-crystal and powder diffraction, respectively. No evidence of phase transition has been observed within the pressure and temperature range investigated. P–V data fitted with an isothermal third-order Birch–Murnaghan equation of state (BM-EoS) give V 0 = 457.1(2) ?3, K T0 = 76(3)GPa, and K′ = 10.6(15). The evolution of the “Eulerian finite strain” versus “normalized stress” shows a linear positive trend. The linear regression yields Fe(0) = 76(3) GPa as intercept value, and the slope of the regression line leads to a K′ value of 10.6(8). The evolution of the lattice parameters with pressure is significantly anisotropic [β(a) = 1/3K T0(a) = 0.0023(1) GPa−1; β(b) = 1/3K T0(b) = 0.0018(1) GPa−1; β(c) = 1/K T0(c) = 0.0072(3) GPa−1]. The β-angle increases in response to the applied P, with: βP = β0 + 0.033(4)P (P in GPa). The structure refinements of clintonite up to 10.1 GPa show that, under hydrostatic pressure, the structure rearranges by compressing mainly isotropically the inter-layer Ca-polyhedron. The bulk modulus of the Ca-polyhedron, described using a second-order BM-EoS, is K T0(Ca-polyhedron) = 41(2) GPa. The compression of the bond distances between calcium and the basal oxygens of the tetrahedral sheet leads, in turn, to an increase in the ditrigonal distortion of the tetrahedral ring, with ∂α/∂P ≈ 0.1°/GPa within the P-range investigated. The Mg-rich octahedra appear to compress in response to the applied pressure, whereas the tetrahedron appears to behave as a rigid unit. The evolution of axial and volume thermal expansion coefficient α with temperature was described by the polynomial α(T) = α0 + α1 T −1/2. The refined parameters for clintonite are as follows: α0 = 2.78(4) 10−5°C−1 and α1 = −4.4(6) 10−5°C1/2 for the unit-cell volume; α0(a) = 1.01(2) 10−5°C−1 and α1(a) = −1.8(3) 10−5°C1/2 for the a-axis; α0(b) = 1.07(1) 10−5°C−1 and α1(b) = −2.3(2) 10−5°C1/2 for the b-axis; and α0(c) = 0.64(2) 10−5°C−1 and α1(c) = −7.3(30) 10−6°C1/2for the c-axis. The β-angle appears to be almost constant within the given T-range. No structure collapsing in response to the T-induced dehydroxylation was found up to 960°C. The HP- and HT-data of this study show that in clintonite, the most and the less expandable directions do not correspond to the most and the less compressible directions, respectively. A comparison between the thermoelastic parameters of clintonite and those of true micas was carried out.  相似文献   

14.
The thermoelastic parameters of synthetic Ca3Al2Si3O12 grossular garnet were examined in situ at high-pressure and high-temperature by energy dispersive X-ray diffraction, using a Kawai-type multi-anvil press apparatus coupled with synchrotron radiation. Measurements have been conducted at pressures up to 20 GPa and temperatures up to 1,650 K: this P, T range covered the entire high-P, T stability field of grossular garnet. The analysis of room temperature data yielded V 0,300 = 1,664 ± 2 ?3 and K 0 = 166 ± 3 GPa for K￠0 K^{\prime}_{0} fixed to 4.0. Fitting of our P–V–T data by means of the high-temperature third order Birch–Murnaghan or the Mie–Grüneisen–Debye thermal equations of state, gives the thermoelastic parameters: (∂K 0,T /∂T) P  = −0.019 ± 0.001 GPa K−1 and α 0,T  = 2.62 ± 0.23 × 10−5 K−1, or γ 0 = 1.21 for fixed values q 0 = 1.0 and θ 0 = 823 (Isaak et al. Phys Chem Min19:106–120, 1992). From the comparison of fits from two different approaches, we propose to constrain the bulk modulus of grossular garnet and its pressure derivative to K T0 = 166 GPa and K￠T0 K^{\prime}_{T0}  = 4.03–4.35. Present results are compared with previously determined thermoelastic properties of grossular-rich garnets.  相似文献   

15.
The high-pressure X-ray diffraction study of a natural arsenopyrite was investigated up to 28.2 GPa using in situ angle-dispersive X-ray diffraction and a diamond anvil cell at National Synchrotron Light Source, Brookhaven National Laboratory. The 16:3:1 methanol–ethanol–water mixture was used as a pressure-transmitting medium. Pressures were measured using the ruby-fluorescence method. No phase change has been observed up to 28.2 GPa. The isothermal equation of state (EOS) was determined. The values of K 0, and K′ 0 refined with a third-order Birch–Murnaghan EOS are K 0 = 123(9) GPa, and K′ 0 = 5.2(8). Furthermore, we confirm that the linear compressibilities (β) along a, b and c directions of arsenopyrite is elastically isotropic (β a  = 6.82 × 10−4, β b  = 6.17 × 10−4 and β c  = 6.57 × 10−4 GPa−1).  相似文献   

16.
An in situ high pressure powder diffraction study, using high-brilliance synchrotron radiation, on lead feldspar (PbAl2Si2O8) was performed. Two samples, with Q od=0.68 and 0.76, were loaded in a diamond anvil cell and were compressed up to 11 GPa. Up to P=7.1 GPa the only phase present is lead feldspar. In the range 7.1–9.4 GPa sudden changes in the position of the reflections suggest the transformation of lead feldspar to a new phase (probably feldspar-like). The absence of split that would be compatible with triclinic symmetry rules out the monoclinic-triclinic transition, that was reported for the structurally similar strontium feldspar. At P>9.4 GPa some new extra reflections not indexable in the feldspar cell are present as well. During decompression the lead feldspar was the only phase present at P<6 GPa. Peak enlargement was observed with pressure, probably preliminary to amorphization. However almost complete amorphization was observed only after fortuitous shock compression at ∼18 GPa; the crystallinity was recovered at room pressure after decompression. The bulk modulus for lead feldspar was K=71.0(9) and 67.6(1.2) GPa for the two samples, in the range reported for feldspars. The cell parameters show a compression pattern which is similar to that observed in anorthite, with Δa/a 0>Δc/c 0>Δb/b 0; comparison with the high temperature behaviour shows that for lead feldspar the strain tensor with pressure is more isotropic and the deformation along a is less prominent. A turnover in the behaviour of the β angle with pressure suggests a change in the compression behaviour at P∼2 GPa. Rietveld refinement of the Pb coordinates was performed in a series of spectra with pressure ranging from 0.6 to 6.5 GPa. The combined analysis of cell parameters and Pb coordinates with pressure showed that the compression of the structure is mainly achieved by an approach of Pb atoms along a *. Received: 21 July 1998 / Revised, accepted: 13 October 1998  相似文献   

17.
The high-pressure behavior of three synthetic amphiboles crystallized with space group P21/m at room conditions in the system Li2O–Na2O–MgO–SiO2–H2O has been studied by in situ synchrotron infrared absorption spectroscopy. The amphiboles have compositions ANa B(Na x Li1 − x Mg1) CMg5 Si8 O22(OH)2 with x = 0.6, 0.2 and 0.0, respectively. The high-P experiments up to 32 GPa were carried out on the U2A beamline at Brookhaven National Laboratory (NY, USA) using a diamond anvil cell under non-hydrostatic or quasi-hydrostatic conditions. The two most intense absorption bands in the OH-stretching infrared spectra can be assigned to two non-equivalent O–H dipoles in the P21/m structure, bonded to the same local environment M1M3Mg3–OH–ANa, and pointing toward two differently kinked tetrahedral rings. In all samples these bands progressively merge to give a unique symmetrical absorption with increasing pressure, suggesting a change in symmetry from P21/m to C2/m. The pressure at which the transition occurs appears to be linearly correlated to the aggregate B-site dimension. The infrared spectra collected for amphibole B(Na0.2Li0.8Mg1) in the frequency range 50 to 1,400 cm−1 also show a series of changes with increasing pressure. The data reported here support the inference of Iezzi et al. (Am Miner 91:479–482, 2006a) regarding a new high-pressure amphibole polymorph.  相似文献   

18.
 Synthetic Zn-ferrite (ideally ZnFe2O4; mineral name: franklinite) was studied up to 37 GPa, by X-ray powder diffraction at ESRF (Grenoble, France), on the ID9 beamline; high pressure was achieved by means of a DAC. The P-V equation of state of franklinite was investigated using the Birch-Murnaghan function, and the elastic properties thus inferred [K0 = 166.4(±3.0) GPa K0 ′ = 9.3(±0.6) K0 ″ = −0.22 GPa−1] are compared with earlier determinations for MgAl-spinel and magnetite. The structural behaviour of Zn-ferrite as a function of pressure was studied by Rietveld refinements, and interpreted in the light of a phase transition from spinel to either CaTi2O4- or MnFe2O4-like structure; this transformation occurs above 24 GPa. Received: 15 March 1999 / Accepted: 22 April 2000  相似文献   

19.
 Synchrotron X-ray powder diffraction experiments at high pressure conditions (0.0001–13 GPa) were performed at ESRF (Grenoble-F), on the beamline ID9, to investigate the bulk elastic properties of natural P2/n-omphacites, with quasi-ideal composition. The monoclinic cell parameters a, b, c and β were determined as a function of pressure, and their compressibility coefficients are 0.00277(7), 0.00313(8), 0.00292(5) and 0.00116(4) GPa−1, respectively. The third-order Birch-Murnaghan equation of state was used to interpolate the experimental P−V data, obtaining K 0=116.6(±2.5) GPa and K′0=6.03(±0.60). K 0 was also determined by means of the axial and angular compressibilities [122.5(±1.7) GPa], and of the finite Lagrangian strain theory [121.5(±1.0) GPa]. The discrepancies on K 0 are discussed in the light of a comparison between techniques to determine the bulk modulus of crystalline materials from static compression diffraction data. Received: 22 February 2000 / Accepted: 10 July 2000  相似文献   

20.
The high-pressure behavior of the lattice elasticity of spodumene, LiAlSi2O6, was studied by static compression in a diamond-anvil cell up to 9.3 GPa. Investigations by means of single-crystal XRD and Raman spectroscopy within the hydrostatic limits of the pressure medium focus on the pressure ranges around ~3.2 and ~7.7 GPa, which have been reported previously to comprise two independent structural phase transitions. While our measurements confirm the well-established first-order C2/c–P21/c transformation at 3.19 GPa (with 1.2% volume discontinuity and a hysteresis between 0.02 and 0.06 GPa), both unit-cell dimensions and the spectral changes observed in high-pressure Raman spectra give no evidence for structural changes related to a second phase transition. Monoclinic lattice parameters and unit-cell volumes at in total 59 different pressure points have been used to re-calculate the lattice-related properties of spontaneous strain, volume strain, and the bulk moduli as a function of pressure across the transition. A modified Landau free energy expansion in terms of a one component order parameter has been developed and tested against these experimentally determined data. The Landau solution provides a much better reproduction of the observed anomalies than any equation-of-state fit to data sets truncated below and above P tr, thus giving Landau parameters of K 0 = 138.3(2) GPa, K′ = 7.46(5), λ V  = 33.6(2) GPa, a = 0.486(3), b = −29.4(6) GPa and c = 551(11) GPa.  相似文献   

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