High-pressure behavior of synthetic mordenite-Na: an in situ single-crystal synchrotron X-ray diffraction study

The high-pressure behavior of a synthetic mordenite- Na (space group: Cmcm or Cmc21) was studied by in situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell up to 9.22(7) GPa. A phase transition, likely displacive in character, occurred between 1.68(7) and 2.70(8) GPa, from a C-centered to a primitive space group: possibly Pbnm, Pbnn or Pbn21. Fitting of the experimental data with III-BM equations of state allowed to describe the elastic behavior of the high-pressure polymorph with a primitive lattice. A very high volume compressibility [KV0 = 25(2) GPa, \u3b2V0 = 1/KV0 = 0.040(3) GPa\u20131; KV\u2032 = ( 02KV/ 02P)T = 2.0(3)], coupled with a remarkable elastic anisotropy (\u3b2b > > \u3b2c > \u3b2a), was found. Interestingly, the low-P and high-P polymorphs show the same anisotropic compressional scheme. A structure collapse was not observed up to 9.22(7) GPa, even though a strong decrease of the number of observed reflections at the highest pressures suggests an impending amorphization. The structure refinements performed at room-P, 0.98(2) and 1.68(7) GPa allowed to describe, at a first approximation, the mechanisms that govern the framework deformation in the low-P regime: the bulk compression is strongly accommodated by the increase of the ellipticity of the large 12-membered ring channels running along [001]

On the P-induced behavior of the zeolite phillipsite : an in situ single-crystal synchrotron X-ray diffraction study

The elastic behavior and the structural evolution at high pressure of a natural phillipsite have been investigated by in situ single-crystal X-ray diffraction up to 9.44 GPa, using a diamond anvil cell and the nominally penetrating P-transmitting fluid methanol:ethanol:water (16:3:1) mix. Although no phase transition was observed within the P-range investigated, two different compressional regimes occur. Between 0.0001 and 2.0 GPa, the refined elastic parameters, calculated by a second-order Birch\u2013Murnaghan equation of state (BM-EoS) fit, are V0 = 1005(1) \uc53, K0 = 89(8) GPa for the unit-cell volume; a0 = 9.914(7) \uc5, Ka = 81(12) GPa for the a-axis; b0 = 14.201(9) \uc5, Kb = 50(5) GPa for the b-axis; and c0 = 8.707(2) \uc5, Kc = 107(8) GPa for the c-axis (Ka:Kb:Kc ~1.62:1:2.14). Between 2.0 and 9.4 GPa, a P-induced change in the configuration of H2O molecules, coupled with a change in the tilting mechanisms of the framework tetrahedra, gives rise to a second compressional regime, in which the phillipsite structure is softer if compared to the first compressional range. In the second compressional regime, the refined elastic parameters, calculated by a second-order BM-EoS fit, are V0 = 1098 (7) \uc53, K0 = 18.8(7) GPa for the unit-cell volume; a0 = 10.07(3) \uc5, Ka = 30(2) GPa for the a-axis; b0 = 14.8(1) \uc5, Kb = 11(1) GPa for the b-axis; and c0 = 8.94(2) \uc5, Kc = 21(1) GPa for the c-axis (Ka:Kb:Kc ~2.72:1:1.90). The evolution of the monoclinic \u3b2 angle with pressure shows two distinct trends in the two compressional regimes: with a negative slope between 0.0001 and 2.0 GPa, and a positive slope between 2.0 and 9.4 GPa. The mechanisms, at the atomic scale, that govern the two compressional regimes of the phillipsite structure are described

Pargasite at high pressure and temperature

The P-T phase stability field, the thermoelastic behavior and the P-induced deformation mechanisms at the atomic scale of pargasite crystals, from the "phlogopite peridotite unit" of the Finero mafic-ultramafic complex (Ivrea-Verbano Formation, Italy), have been investigated by a series of in situ experiments: (a) at high pressure (up to 20.1 GPa), by single-crystal synchrotron X-ray diffraction with a diamond anvil cell, (b) at high temperature (up to 823 K), by powder synchrotron X-ray diffraction using a hot air blower device, and (c) at simultaneous HP-HT conditions, by single-crystal synchrotron X-ray diffraction with a resistive-heated diamond anvil cell (Pmax = 16.5 GPa, Tmax = 1200 K). No phase transition has been observed within the P-T range investigated. At ambient T, the refined compressional parameters, calculated by fitting a second-order Birch-Murnaghan Equation of State (BM-EoS), are: V0 = 915.2(8) \uc53 and KP0,T0 = 95(2) GPa (\u3b2P0,T0 = 0.0121(2) GPa-1) for the unit-cell volume; a0 = 9.909(4) \uc5 and K(a)P0,T0 = 76(2) GPa for the a-axis; b0 = 18.066(7) \uc5 and K(b)P0,T0 = 111(2) GPa for the b-axis; c0 = 5.299(5) \uc5 and K(c)P0,T0 = 122(12) GPa for the c-axis [K(c)P0,T0 ~ K(b)P0,T0 > K(a)P0,T0]. The high-pressure structure refinements (at ambient T) show a moderate contraction of the TO4 double chain and a decrease of its bending in response to the hydrostatic compression, along with a pronounced compressibility of the A- and M(4)-polyhedra [KP0,T0(A) = 38(2) GPa, KP0,T0(M4) = 79(5) GPa] if compared to the M(1)-, M(2)-, M(3)-octahedra [KP0,T0(M1,2,3) 64 120 GPa] and to the rigid tetrahedra [KP0,T0(T1,T2) ~ 300 GPa]. The thermal behavior, at ambient pressure up to 823 K, was modelled with Berman's formalism, which gives: V0 = 909.1(2) \uc53, \u3b10 = 2.7(2)*10-5 K-1 and \u3b11 = 1.4(6)*10-9 K-2 [with \u3b10(a) = 0.47(6)*10-5 K-1, \u3b10(b) = 1.07(4)*10-5 K-1, and \u3b10(c) = 0.97(7)*10-5 K-1]. The petrological implications for the experimental findings of this study are discussed

High-pressure behavior and P-induced phase transition of CaB3O4(OH)3·H2O (colemanite)

Colemanite (ideally CaB3O4(OH)3\ub7H2O, space group P21/a, unit-cell parameters: a ~ 8.74, b ~ 11.26, c ~ 6.10 \uc5, \u3b2 ~ 110.1\ub0) is one of the principal mineralogical components of borate deposits and the most important mineral commodity of boron. Its high-pressure behavior is here described, for the first time, by means of in situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell up to 24 GPa (and 293 K). Colemanite is stable, in its ambient-conditions polymorph, up to 13.95 GPa. Between 13.95 and 14.91 GPa, an iso-symmetric first-order single-crystal to single-crystal phase transition (reconstructive in character) toward a denser polymorph (colemanite-II) occurs, with: aCOL-II=3\ub7aCOL, bCOL-II=bCOL, and cCOL-II=2\ub7cCOL. Up to 13.95 GPa, the bulk compression of colemanite is accommodated by the Ca-polyhedron compression and the tilting of the rigid three-membered rings of boron polyhedra. The phase transition leads to an increase in the average coordination number of both the B and Ca sites. A detailed description of the crystal structure of the high-P polymorph, compared to the ambient-conditions colemanite, is given. The elastic behaviors of colemanite and of its high-P polymorph are described by means of III- and II-order Birch-Murnaghan equations of state, respectively, yielding the following refined parameters: KV0=67(4) GPa and KV\u2032=5.5(7) [\u3b2V0=0.0149(9) GPa-1] for colemanite; KV0=50(8) GPa [\u3b2V0=0.020(3) GPa-1] for its high-P polymorph

Deformation of NaCoF3 perovskite and post-perovskite up to 30 GPa and 1013 K: implications for plastic deformation and transformation mechanism

Texture, plastic deformation, and phase transformation mechanisms in perovskite and post-perovskite are of general interest for our understanding of the Earth's mantle. Here, the perovskite analogue NaCoF3 is deformed in a resistive-heated diamond anvil cell (DAC) up to 30 GPa and 1013 K. The in situ state of the sample, including crystal structure, stress, and texture, is monitored using X-ray diffraction. A phase transformation from a perovskite to a post-perovskite structure is observed between 20.1 and 26.1 GPa. Normalized stress drops by a factor of 3 during transformation as a result of transient weakening during the transformation. The perovskite phase initially develops a texture with a maximum at 100 and a strong 010 minimum in the inverse pole figure of the compression direction. Additionally, a secondary weaker 001 maximum is observed later during compression. Texture simulations indicate that the initial deformation of perovskite requires slip along (100) planes with significant contributions of {110} twins. Following the phase transition to post-perovskite, we observe a 010 maximum, which later evolves with compression. The transformation follows orientation relationships previously suggested where the c axis is preserved between phases and hh0 vectors in reciprocal space of post-perovskite are parallel to [010] in perovskite, which indicates a martensitic-like transition mechanism. A comparison between past experiments on bridgmanite and current results indicates that NaCoF3 is a good analogue to understand the development of microstructures within the Earth's mantle

Universal phase transitions of B1 structured stoichiometric transition-metal carbides

The high-pressure phase transitions of B1-structured stoichiometric transition metal carbides (TMCs, TM=Ti, Zr, Hf, V, Nb, and Ta) were systematically investigated using ab initio calculations. These carbides underwent universal phase transitions along two novel phase-transition routes, namely, B1\rightarrowdistorted TlI (TlI')\rightarrowTlI and/or B1\rightarrowdistorted TiB (TiB')\rightarrowTiB, when subjected to pressures. The two routes can coexist possibly because of the tiny enthalpy differences between the new phases under corresponding pressures. Four new phases result from atomic slips of the B1-structured parent phases under pressure. After completely releasing the pressure, taking TiC as a representative of TMCs, only its new TlI'-type phase is mechanically and dynamically stable, and may be recovered.Comment: [email protected]

High-pressure behavior and phase stability of Na2B4O6(OH)2·3H2O (kernite)

The high-pressure behavior of kernite [ideally Na2B4O6(OH)2\ub73H2O, a ~ 7.02 \u212b, b ~ 9.16 \u212b, c ~ 15.68 \u212b, \u3b2 = 108.9\ub0, Sp Gr P21/c, at ambient conditions], an important B-bearing raw material (with B2O3 48 51 wt%) and a potential B-rich aggregate in radiation shielding materials, has been studied by single-crystal synchrotron X-ray diffraction up to 14.6 GPa. Kernite undergoes an iso-symmetric phase transition at 1.6-2.0 GPa (to kernite-II). Between 6.6-7.5 GPa, kernite undergoes a second phase transition, possibly iso-symmetric in character (to kernite-III). The crystal structure of kernite-II was solved and refined. The isothermal bulk modulus (KV0 = \u3b2-1 P0,T0, where \u3b2P0,T0 is the volume compressibility coefficient) of the ambient-pressure polymorph of kernite was found to be KV0 = 29(1) GPa and a marked anisotropic compressional pattern, with K(a)0: K(b)0: K(c)0~1:3:1.5., was observed. In kernite-II, the KV0 increases to 43.3(9) GPa and the anisotropic compressional pattern increases pronouncedly. The mechanisms, at the atomic scale, which govern the structure deformation, have been described

Pressure-induced structural change in liquid GaIn eutectic alloy

Synchrotron x-ray diffraction reveals a pressure induced crystallization at about 3.4 GPa and apolymorphic transition near 10.3 GPa when compressed a liquid GaIn eutectic alloy up to ~13 GPa atroom temperature in a diamond anvil cell. Upon decompression, the high pressure crystalline phaseremains almost unchanged until it transforms to the liquid state at around 2.3 GPa. The ab initiomolecular dynamics calculations can reproduce the low pressure crystallization and give some hints onthe understanding of the transition between the liquid and the crystalline phase on the atomic level.The calculated pair correlation function g(r) shows a non-uniform contraction reflected by the differentcompressibility between the short (1st shell) and the intermediate (2nd to 4th shells). It is concludedthat the pressure-induced liquid-crystalline phase transformation likely arises from the changes in localatomic packing of the nearest neighbors as well as electronic structures at the transition pressure