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Abstract The high-pressure behavior of a natural ettringite [Ca 6 Al 2 (SO 4) 3 (OH) 12 ·27H 2 O, a = 11.2104(2) Å, c = 21.4350(3) Å, sp. gr. P 31 c ] has been studied by single-crystal X-ray diffraction with a diamond-anvil cell up to 4.22 GPa, using the methanol:ethanol = 4:1 mixture as a hydrostatic pressure-transmitting fluid. The isothermal bulk modulus (K 0 = − V (∂ P / ∂ V)) was found to be 26.6(5) GPa. Ettringite shows a significant anisotropic compressional pattern, being more compressible on (001) than along [001] (i.e. the fibers growing axis), with K (c) 0 ~ 2 K (a , b) 0. The mechanisms at the atomic scale, which govern the structure deformation, have been described by a series of structure refinements up to 2.3 GPa. The structure evolution in response to the applied pressure indicates a plausible densification of the hydrogen-bond network between the Ca(OH) 4 (H 2 O) 4 polyhedra and the SO 4 tetrahedra, which results in a softening and ultimately in a collapse of the whole structure at pressures > 3 GPa. Graphical abstract Unlabelled Image Highlights • The anisotropic elastic behavior of ettringite has been investigated up to 4.2 GPa. • Above 3 GPa, a sharp softening of the structure, mainly on the ab plane occurs. • Such softening may be induced by a collapse of the hydrogen bonds network. [ABSTRACT FROM AUTHOR]

The high-pressure behavior of monovalent-cation-exchanged chabazites was investigated by means of in situ synchrotron X-ray powder diffraction with a diamond-anvil cell, and using water as penetrating pressure-transmitting medium, up to 5.5 GPa at room temperature. In all cases, except for Na-containing chabazites, a phase transition from the original rhombohedral (R 3 m) to triclinic symmetry (likely P 1 ) was observed in the range between 3.0 GPa and 5.0 GPa. The phase transition is accompanied by an abrupt decrease of the unit-cell volume by up to 10%. Evidence of pressure-induced hydration (PIH), i.e., P-induced penetration of H2O molecules through the zeolitic cavities, was observed, as reflected by the incompressibility of the cation-exchanged chabazites, which is governed by the distribution of the extra-framework cations. The reversibility of the PIH and P-induced phase transitions in the high-pressure behavior of the cation-exchanged chabazites are discussed in the context of the role played by the chemical nature and bonding configuration of the extra-framework cations, along with that of the H2O content at room conditions. [ABSTRACT FROM AUTHOR]

This is a review of the thermal and compressional behavior of cancrinite-group minerals with a description of the mechanisms, at the atomic scale, that govern their P-T-induced structure evolution. The open-framework structure of this group of feldspathoids is characterized by the [CAN] topology, which contains large parallel channels (confined by 12-membered rings of tetrahedra), surrounded by columns of cages. At least two structural "subgroups" can be identified according to the nature of the constituents filling the cages, irrespective of the channel population. The minerals of the "cancrinite subgroup" show [NaH2O]+ clusters into the cages and those of the "davyne subgroup" contains [CaCl]+ clusters. Beside a similar bulk compressibility and expansivity at room conditions for all the minerals of the group, a different elastic anisotropy, coupled with different deformation mechanisms of the tetrahedral framework, were found to be mainly controlled by the nature of the population filling the cages. The role played by the channel populations appears to be secondary. These experimental findings allow us to provide a model of the structure evolution in response to the different cage content, i.e., NaH2O+ and CaCl+. The high-temperature studies of the hydrous members of the cancrinite subgroup reveal a slow dehydration process, often irreversible at the timescale of the experiments and leading to quasi-anhydrous high-temperature forms that keep their crystallinity even up to 800-900 K (at room P). The experiments at high pressure on the cancrinite-group minerals show a high-P stability, at least up to 7-8 GPa (at room-T), which is quite surprising if we consider their microporous nature. The P-induced stability is the effect of a pronounced structural flexibility, which in turn is based mainly on tilting of rigid tetrahedra around O atoms that behave as hinges. The character and the mechanisms that govern the P-T-induced P63-to-P63/m phase transition in the compounds of davyne subgroup are also discussed. [ABSTRACT FROM AUTHOR]

The compressional behavior and the P -induced crystal–fluid interaction of a natural paulingite-K have been explored on the basis of in-situ single-crystal and powder X-ray diffraction, and in-situ single-crystal Raman spectroscopy with a diamond anvil cell and a series of diverse pressure-transmitting fluids ( i.e. , silicone-oil, methanol:ethanol = 4:1, methanol:ethanol:water = 16:3:1). No evidence of any phase transition was observed within the P -range investigated, independent on the used P -fluids. The compressional behavior of paulingite is significantly different in response to the different nature of the P -fluids. A drastically lower compressibility is observed when the zeolite is compressed in methanol:ethanol or, even more noticeably, in methanol:ethanol:water mix. We ascribe this phenomenon to the different crystal–fluid interaction at high pressure: (1) silicone-oil is a “non-penetrating” P -medium, because of its polymeric nature, whereas (2) methanol–ethanol and water are “penetrating” P -fluids. The P -induced penetration processes appear to be completely reversible on the basis of the X-ray diffraction data alone. The Raman spectra collected after the high-pressure experiments show, unambiguously, that a residual fraction of methanol (and/or ethanol and probably even extra H 2 O) still resides in the zeolitic sub-nanocavities; such molecules are spontaneously released after a few days at atmospheric pressure. The actual compressibility of paulingite-K is that obtained by the compression experiment in silicone-oil, with an isothermal bulk modulus K 0 = β 0 −1 = 18.0(1.1) GPa. Paulingite appears to be one of the softest zeolite ever found. [ABSTRACT FROM AUTHOR]

The high-pressure behavior of cordierite was investigated by means of in situ experiments using piston-cylinder press and diamond-anvil cell. Static compression in diamond-anvil cells was conducted with various penetrating and non-penetrating pressure media (H2O up to 2 GPa, argon and 4:1-methanolethanol up to 7 GPa). The measurement of lattice parameters revealed neither a significant influence on the elasticity nor any indication for effects in analogy to over-hydration within the experimental pressure ranges. Volumetric compression experiments at constant rates up to 1.2 GPa in a piston-cylinder apparatus insinuate subtle irregularities in the low-pressure range at around ~0.35 and ~0.85 GPa. The ΔV/V contribution related to the anomalous compression behavior in that pressure range is of the order of 5 x 10-4. The results obtained from single-crystal X-ray diffraction between 10-4 and 7 GPa revealed an unexpected and anomalous linear volume decrease, corresponding to KT,298 = 131±1 GPa for the bulk modulus and K' = -0.4±0.3 for its pressure derivative for a third-order Birch-Murnaghan equation of state. The compressional behavior of the main axis directions is anisotropic with βa-1 ≈ βb-1 > βc-1 for an initial pressure regime up to ~3 GPa. At pressures above ~4 GPa, the compression of the a- and b-axis starts to differ significantly, with the b-axis showing elastic softening as indicated by negative values for ∂(βb-1)∂P. The diversification between the a- and b-axis is also expressed by the pressure-depending increase of the distortion parameter Δ. The pronounced elastic softening in both the b-axis and c-axis directions ∂(βb-1)/∂P = -4.3±0.9, ∂(βc-1)/∂P = -1.2±0.8) are responsible for the apparent linear bulk compression, which indicates the structural instability and precedes a so far not reported ferroelastic phase transition to a triclinic polymorph, following a primitive lattice above the critical transition at ~6.9 GPa. [ABSTRACT FROM AUTHOR]

Abstract: An in situ high-pressure single-crystal X-ray diffraction study of gobbinsite, the natural counterpart of the synthetic zeolite Na–P2, was carried out up to 4.3GPa. No evidence of amorphization was observed within pressure-range investigated. Using a non-penetrating P-medium, two changes of the elastic behavior occur: the first at 1.1–1.3GPa and the second at 2.7–3.2GPa. Birch-Murnaghan equations of state truncated to the second order were used to fit the experimental P–V data within the three P-ranges (i.e. 0.0001–1.1, 1.3–2.7 and 3.2–4.3GPa), giving the following isothermal bulk moduli (KV 0): 46.3(9), 52(8) and 28(6) GPa, respectively. The unit-cell compression is significantly anisotropic. In response to the applied pressure, the 8-membered ring channel parallel to [100] undergoes a significant increase of ellipticity, whereas the channel parallel to [010] undergoes a shrinking towards a circular shape at P ≥1.3GPa. A partial re-organization of the H2O sites occurs between 1.1 and 1.3GPa, and new framework deformational modes onset at P ≥3.2GPa, coupled with a change in the coordination environment of the extraframework cations. [Copyright &y& Elsevier]

Abstract: The thermo-elastic behavior and the P/T-induced structure evolution of a synthetic CsAlSiO4 [ABW framework type, with Pc21 n space group and lattice parameters: a =9.414(1), b =5.435(1), c =8.875(1)Å at room conditions] have been investigated up to 1000°C (at 0.0001GPa) and up to 10GPa (at 20°C) by means of in-situ synchrotron powder diffraction. No phase transition has been observed within the temperature- and pressure-range investigated. P–V data were fitted with a third-order Birch–Murnaghan Equation of State (BM-EoS), giving: V 0 =457.9(4)Å3, K T0 =42(1)GPa and K′=3.9(3) (with a second-order Birch–Murnaghan Equation of State: V 0 =458.1(2)Å3, K T0 =41.3(3)GPa). The evolution of the “Eulerian finite strain” vs. “normalized stress” yields Fe(0)=41.9(5)(1)GPa as intercept values, with an almost horizontal slope of the regression line. The evolution of the lattice parameters with pressure shows a remarkably anisotropic compressional pattern, along with subtle change in the axial elastic behavior along [100] and [010] at P >4GPa. The elastic parameters calculated with a “linearized” BM-EoS are: K T0(a)=244(11)GPa for the a-axis (K(a)′=4); K T0(b)=181(3)GPa for the b-axis (K(b)′=4), and K T0(c)=14.5(5) GPa and K(c)′ = 2.6(1) for the c-axis. The volume thermal expansion with T was described by the polynomial function: V(T)/V 0 =1+α0·T +α1·T 2 =1+3.63(1)×10−5·T −3.8(1)×10−9·T 2. The structure reacts, in response to the applied T, by a negative thermal expansion along [100] (i.e. α0(a)=−9.97(1)×10−6 °C−1), almost no expansion along [010] (i.e. α0(b)=0.36(1)×10−6 °C−1) and a pronounced positive expansion along [001] (i.e. α0(c)=47.46(6)×10−6 °C−1). The main P/T-induced structure deformation mechanisms, at the atomic level, are discussed. [Copyright &y& Elsevier]

The high-pressure elastic behavior and the P-induced structure evolution of a natural cancrinite from Cameroun {Na6.59Ca0.93[Si6Al6O24](CO3)1.04F0.41·2H2O, a = 12.5976(6) Å, c = 5 .1168(2) Å, space group: P63} were investigated by in situ single-crystal X-ray diffraction under hydrostatic conditions up to 6.63(2) GPa with a diamond-anvil cell. The P-V data were fitted with an isothermal Birch-Murnaghan type equation of state (BM EoS) truncated to the third order. Weighted fit (by the 3 uncertainty in P and V) gave the following elastic parameters: V0 = 702.0(7) Å , KV0 = 51(2) GPa, and Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. = 2.9(4). A linearized BM EoS was used to fit the a-P and c-P data, giving the following refined parameters: a0 = 12.593(5) Å, Ka0 = 64(4) GPa, Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. = 4.5(9), for the a-axis, and c0 = 5.112(3) Å, Kc0 = 36(1) GPa, Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. = 1.9(3) for the c c-axis (elastic anisotropy: Ka0:Kc0 = 1.78:1). A subtle change of the elastic behavior appears to occur at P > 4.62 GPa, and so the elastic behavior was also described on the basis of BM EOS valid between 0.0001-4.62 and 5.00-6.63 GPa, respectively. The high-pressure structure refinements allowed the description of the main deformation mechanisms responsible for the anisotropic compression of cancrinite on (0001) and along [0001]. A comparative analysis of the structure evolution in response of the applied pressure and temperature of isotypic materials with cancrinite-like topology is carried out. [ABSTRACT FROM AUTHOR]

The phase stability, elastic behavior, and pressure-induced structural evolution of a natural metamorphic kalsilite (ideal formula KAlSiO4) from Punalur (Kerala district in southern India), with P31c symmetry and a K/Na molar ratio of ~350, has been investigated by in situ X-ray single-crystal diffraction up to ~7 GPa with a diamond-anvil cell under hydrostatic conditions. At high-pressure, a previously unreported iso-symmetric first-order phase transition occurs at ~3.5 GPa. The volume compression of the two phases is described by third-order Birch-Murnaghan equations-of-state: V0 = 201.02(1) ų, KT0 = 59.7(5) GPa, K' = 3.5(3) for the low-P polymorph, and V0 = 200.1(13) ų, KT0 = 44(8) GPa, K' = 6.4(20) for the high-P polymorph. The pressure-induced structural evolution in kalsilite up to 7 GPa appears to be completely reversible. The compression of both phases involves tetrahedral rotations around [0001], which close up the channels within the framework. In addition, compression of the low-pressure phase involves tilting of the tetrahedra. The major structural change at the phase transition is an increase in the tilting of the tetrahedra, but with a reversion of the tetra-hedral rotations to the value found at ambient conditions. This behavior is in distinct contrast to that of nepheline, which has a tetrahedral framework of the same topology. [ABSTRACT FROM AUTHOR]

The thermo-elastic behavior of a natural epidote [Ca FeAlTiSiO(OH)] has been investigated up to 1,200 K (at 0.0001 GPa) and 10 GPa (at 298 K) by means of in situ synchrotron powder diffraction. No phase transition has been observed within the temperature and pressure range investigated. P- V data fitted with a third-order Birch-Murnaghan equation of state (BM-EoS) give V = 458.8(1)Å, K = 111(3) GPa, and K′ = 7.6(7). The confidence ellipse from the variance-covariance matrix of K and K′ from the least-square procedure is strongly elongated with negative slope. The evolution of the 'Eulerian finite strain' vs 'normalized stress' yields Fe(0) = 114(1) GPa as intercept values, and the slope of the regression line gives K′ = 7.0(4). The evolution of the lattice parameters with pressure is slightly anisotropic. The elastic parameters calculated with a linearized BM-EoS are: a = 8.8877(7) Å, K( a) = 117(2) GPa, and K′( a) = 3.7(4) for the a-axis; b = 5.6271(7) Å, K( b) = 126(3) GPa, and K′( b) = 12(1) for the b-axis; and c = 10.1527(7) Å, K( c) = 90(1) GPa, and K'( c) = 8.1(4) for the c-axis [ K( a): K( b): K( c) = 1.30:1.40:1]. The β angle decreases with pressure, β(°) = β −0.0286(9) P +0.00134(9) P ( P in GPa). The evolution of axial and volume thermal expansion coefficient, α, with T was described by the polynomial function: α( T) = α + α T. The refined parameters for epidote are: α = 5.1(2) × 10 K and α = −5.1(6) × 10 K for the unit-cell volume, α( a) = 1.21(7) × 10 K and α( a) = −1.2(2) × 10 K for the a-axis, α( b) = 1.88(7) × 10 K and α( b) = −1.7(2) × 10 K for the b-axis, and α( c) = 2.14(9) × 10 K and α( c) = −2.0(2) × 10 K for the c-axis. The thermo-elastic anisotropy can be described, at a first approximation, by α( a): α( b): α( c) = 1 : 1.55 : 1.77. The β angle increases continuously with T, with β(°) = β + 2.5(1) × 10 T + 1.3(7) × 10 T. A comparison between the thermo-elastic parameters of epidote and clinozoisite is carried out. [ABSTRACT FROM AUTHOR]

The structural evolution at high pressure of a natural 2 M-phengite [(KNa)(AlMgFeTi)(SiAl)O(OH); a = 5.228(2), b = 9.057(3), c = 19.971(6)Å, β = 95.76(2)°; space group: C2/ c] from the metamorphic complex of Cima Pal (Sesia Zone, Western Alps, Italy) was studied by single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions up to ~11 GPa. A series of 12 structure refinements were performed at selected pressures within the P range investigated. The compressional behaviour of the same phengite sample was previously studied up to ~25 GPa by synchrotron X-ray powder diffraction, showing an irreversible transformation with a drastic decrease of the crystallinity at P > 15–17 GPa. The elastic behaviour between 0.0001 and 17 GPa was modelled by a third-order Birch–Murnaghan Equation of State (BM-EoS), yielding to K = 57.3(10) GPa and K′ = ∂ K/∂ P = 6.97(24). The single-crystal structure refinements showed that the significant elastic anisotropy of the 2 M-phengite (with β( a):β( b):β( c) = 1:1.17:4.60) is mainly controlled by the anisotropic compression of the K-polyhedra. The evolution of the volume of the inter-layer K-polyhedron as a function of P shows a negative slope, Fitting the P– V(K-polyhedron) data with a truncated second-order BM-EoS we obtain a bulk modulus value of K(K-polyhedron) = 26(1) GPa. Tetrahedra and octahedra are significantly stiffer than the K-polyhedron. Tetrahedra behave as quasi-rigid units within the P range investigated. In contrast, a monotonic decrease is observed for the octahedron volume, with K = 120(10) GPa derived by a BM-EoS. The anisotropic response to pressure of the K-polyhedron affects the P-induced deformation mechanism on the tetrahedral sheet, consisting in a cooperative rotation of the tetrahedra and producing a significant ditrigonalization of the six-membered rings. The volume of the K-polyhedron and the value of the ditrigonal rotation parameter (α) show a high negative correlation (about 93%), though a slight discontinuity is observed at P >8 GPa. α increases linearly with P up to 7–8 GPa (with ∂α/∂ P ≈ 0.7°/GPa), whereas at higher Ps a “saturation plateau” is visible. A comparison between the main deformation mechanisms as a function of pressure observed in 2 M- and 3 T-phengite is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The crystal-structure and the high-pressure behavior of a natural cubic melanophlogite (Sp. Gr. Pm3n at room-conditions), a type-I SiO2 clathrate containing only methane as guest gas, was investigated by X-ray single-crystal diffraction at room-conditions and in situ high-pressure synchrotron powder diffraction with a diamond anvil cell and methanol:ethanol:water=16:3:1 (MEW) mixture and silicon-oil (Si-oil) as pressure transmitting media up to about 6GPa. A cubic-to-tetragonal phase-transition was observed at P ⩾1.14GPa, in both MEW and Si-oil runs. The tetragonal polymorph is stable up to the highest pressure in the run with MEW, but it switches back to cubic symmetry at P >3.12GPa in Si-oil. The different elastic behavior is ascribable to the non-hydrostatic conditions in Si-oil medium at P >1GPa. The elastic behavior of melanophlogite was described fitting the P–V data with a Birch–Murnaghan Equation-of-State, showing similar bulk modulus values for the low-pressure cubic and high-pressure tetragonal phases [i.e. K 0,L-cub =23.4(2.4), K 0,tetr =22.2(9)]. The spontaneous strain for the cubic-to-tetragonal transition is almost completely governed by a compression along the c axis, with negligible contribution along a. An inverse behavior is found with respect to the tetragonal-to-cubic high-temperature phase-transition previously described for Mt. Hamilton melanophlogite. A Landau fit of the spontaneous strain (ε ss), related to the order parameter (Q) of the transition as ε ss ∝ Q, showed a first-order character of the P-induced phase-transition and a P c =1.2(3)GPa. Symmetry breaking spontaneous strain prevails respect to the volume strain, which is however present and significant. [Copyright &y& Elsevier]

Abstract: The elastic behaviour and the pressure (P) induced structural evolution of Na6Cs2Ga6Ge6O24 ·Ge(OH)6, a synthetic compound isotypic with cancrinite (CAN topology), have been investigated up to 5.01(5)GPa by means of in situ X-ray synchrotron powder diffraction with a diamond anvil cell and using a nominally penetrating hydrous P-transmitting medium (methanol:ethanol:water=16:3:1). No evidence of phase-transition was observed within the P-range investigated. The P–V data were fitted with a Murnaghan equation-of-state (M-EoS). The elastic parameters obtained, using the data weighted by the uncertainties in P–V, are: V 0 =757.16(7)Å3, K T0 =36(2)GPa [K T0 =1/β =−V 0(∂P/∂V) P=0, where β is the volume compressibility coefficient] and K′=(∂K T0/∂P)=9(1). The elastic behaviour along the a and c axis was described with a “linearised” M-EoS. The refined parameters of the linearised M-EoS are: a 0 =13.0314(4)Å, K T0(a)=40(2) [β j =−1/(3K T0(j))=(1/l 0j )(∂l j /∂P), where β j is the axial compressibility coefficient] and K′(a)=11(1) for the a-axis; c 0 =5.1485(4)Å, K T0(c)=31(1)GPa and K′(c)=7.4(8) for the c-axis. The elastic anisotropy of Na6Cs2Ga6Ge6O24 ·Ge(OH)6 is only marginal, being K T0(a): K T0(c)=1.29:1. The configuration of the extra-framework content is basically maintained at high-pressure, without any major changes. The Ge(OH)6-polyhedron is strongly compressed in response to the applied pressure, but there is no evidence of further deformation. On the other hand the Na(O3OH3)-polyhedron and the large Cs-polyhedron appear to be compressed in a way to lessen the deformation with increasing pressures. Despite the use of a hydrous P-transmitting fluid for the HP-experiment and the large “free-diameters” of the channels in CAN framework, no evidence of superhydration effect was observed within the P-range investigated. [Copyright &y& Elsevier]

Elastic and structural behavior of a natural tetragonal leucite from the volcanic Lazium district (Italy) were investigated at high pressure by in situ single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions. A first-order phase transition, never reported in the literature, was observed at P = 2.4 ± 0.2 GPa from tetragonal (I41/a) to triclinic symmetry (analysis of diffraction intensities suggests the space group P1), accompanied by a drastic increase in density of about 4.7%. The transition pressure was bracketed by several measurements in compression and decompression. No further phase-transition has been observed up to 7 GPa. Fitting a second-order Birch-Murnaghan equation of state (BM-EoS) to the pressure-volume data of the tetragonal polymorph, we obtain K0 = 41.9(6) GPa and K′ = 4 (fixed). In the case of the triclinic polymorph, a second-order BM-EoS gives K0 = 33.2(5) GPa. The eulerian finite strain (fe) vs. normalized stress (Fe) curves were calculated for the low- and high-P polymorphs, providing Fe(0) = 42(1) and Fe(0) = 33.2(4) GPa, respectively. The axial bulk modulus values of the tetragonal polymorph, calculated with a linearized BM-EoS, are K0(a) = 34.5(5) and K0(c) = 78(1) GPa. For the triclinic polymorph, we obtain K0(a) = 35.9(5), K0(b) = 34.9(7), and K0(c) = 35.5(7) GPa. The elastic behavior of the low-P polymorph appears to be more anisotropic than that of the high-P polymorph. The HP-crystal structure evolution of the tetragonal polymorph of leucite was studied on the basis of six structural refinements at different pressures between 0.0001 and 1.8 GPa. The main deformation mechanisms at high-pressure are due to tetrahedral tilting, giving rise to an increase of the ellipticity of the four- and six-membered rings of the tetrahedral framework. The T-O bond distances are practically invariant within the stability field of the tetragonal polymorph. The complex P-induced twinning, due to the tetragonal → triclinic phase-transition, and the low quality of the diffraction data at pressure above the phase-transition, did not allow the refinement of the crystal structure of the triclinic polymorph. [ABSTRACT FROM AUTHOR]

Abstract: The high-pressure (HP) elastic behaviour and the P-induced structural evolution of a natural zeolite phillipsite, K2Ca n Na2−n Al4+n Si12−n O32 ·12H2O (with n ⩽2) [a =9.9291(3), b =14.2621(6), c =8.6920(5)Å, β =124.592(3)°, space group P21/m], has been investigated by in situ synchrotron X-ray powder diffraction up to 3.64GPa using a diamond anvil cell and a nominally penetrating hydrous P-transmitting medium. No phase transition has been observed within the P-range investigated. Axial and volume bulk moduli have been calculated using a truncated second-order Birch–Murnaghan Equation-of-State. The refined elastic parameters are: V 0 =1013.3(1)Å3, K 0 =67(2)GPa [β =0.0149(5)GPa−1] for the unit-cell volume; a 0 =9.9290(7)Å, K(a)=69(2)GPa [β(a)=0.0048(2)GPa−1] for the a-axis; b 0 =14.262(2)Å, K(b)=49(2)GPa [β(b)=0.0068(3)GPa−1] for the b-axis and c 0 =8.691(1)Å, K(c)=111(3)GPa [β(c)=0.00300(8)GPa−1] for the c-axis, with K(a):K(b):K(c)=1.41:1:2.26. The magnitude of the principal unit-strain coefficients, between 0.0001GPa and 3.64GPa, were calculated. The unit-strain ellipsoid is oriented with ε 1∥b, ε 2 and ε 3 lying on the (010) plane with ε 3∠a =115.1(3)° and ∣ε 1∣>∣ε 2∣>∣ε 3∣. The structural refinements performed at high-P allow to explain the reasons of the elastic anisotropy. The cooperative rotation of the tetrahedra increase the ellipticity of the channel systems, maintaining the original elliptical configuration (without any “inversion” in ellipticity). [Copyright &y& Elsevier]

The high-pressure behavior of wardite, NaAl3(PO4)2(OH)4·2H2O (a = 7.0673(2) Å, c = 19.193(9) Å, Sp. Gr. P41212), has been investigated by in-situ single-crystal synchrotron diffraction experiments up to 9 GPa, using a diamond anvil cell under quasi-hydrostatic conditions. This phosphate does not experience any pressure-induced phase transition, or anomalous compressional behavior, within the pressure-range investigated: its compressional behavior is fully elastic and all the deformation mechanisms, at the atomic scale, are reversible upon decompression. A second-order Birch–Murnaghan Equation of State was fitted to the experimental data, weighted by their uncertainty in pressure (P) and volume (V), with the following refined parameters: V0 = 957.8(2) Å3 and KV0 = −V0(∂P/∂V)P0,T0 = 85.8(4) GPa (βV0 = 1/KV0 = 0.01166(5) GPa−1). Axial bulk moduli were also calculated, with: K0(a) = 98(3) GPa (β0(a) = 0.0034(1) GPa−1) and K0(c) = 64(1) GPa (β0(c) = 0.0052(1) GPa−1). The anisotropic compressional scheme is: K0(a):K0(c) = 1.53:1. A series of structure refinements were performed on the basis of the intensity data collected in compression and decompression. The mechanisms at the atomic scale, responsible for the structure anisotropy of wardite, are discussed. [ABSTRACT FROM AUTHOR]

Abstract The high-pressure behavior of a natural armstrongite [(Ca 0.96 Ce 0.01 Yb 0.01)Zr 0.99 Si 6 O 14.97 ·2.02H 2 O, a ∼14.03 Å, b ∼14.14 Å, c ∼7.85 Å, β ∼109.4°, Sp. Gr. C 2/ m ], a microporous heterosilicate, has been studied by single-crystal X-ray diffraction with a diamond-anvil cell up to 8 GPa, using the methanol:ethanol:H 2 O = 16:3:1 mixture as a pressure-transmitting fluid. A first-order phase transition, characterized by a triplication of the unit-cell volume, was detected between 4.01 (5) and 5.07 (5) GPa. The isothermal bulk modulus (K V 0 = - V (∂ P /∂ V)) of the high-pressure polymorph was found to be ∼50% higher than that obtained for the low-pressure one (i.e. , K V 0 = 45 (1) GPa for the high-pressure polymorph, K V 0 = 31.2 (6) GPa for the low-pressure polymorph), indicating a remarkable change in the structure compressibility. The mechanisms at the atomic scale, which govern the structure deformation of the low- P polymorphs, are described based on a series of structure refinements up to 4 GPa, and a comparison with those experienced by the structure at high temperature is provided. As observed for other microporous silicates, the polyhedral tilting is the main deformation mechanism able to accommodate the effects of the applied pressure. No evidence of crystal-fluid interaction, with a selective sorption of molecules of the pressure-transmitting fluid through the cavities, was observed at high pressure. Graphical abstract Image 1 Highlights • The elastic behavior of armstrongite has been investigated up to 8 GPa. • A first-order phase transition has been detected between 4 and 5 GPa. • Polyhedral tilting is the major deformation mechanism at high pressure. [ABSTRACT FROM AUTHOR]

The elastic behavior and the pressure-induced structural evolution of a natural nepheline (K0.54 Na3.24Ca0.03Al4Si4O16) were investigated by in-situ single-crystal X-ray diffraction up to 7.5 GPa with a diamond anvil cell under hydrostatic conditions. As observed in previous studies, at room conditions the diffraction pattern of nepheline includes satellite reflections, whereas the structure refinement to the Bragg reflections confirms that the O1 site is displaced from the triad at (2/3, 1/3, z). The reflection conditions confirm that the space group of the average structure of nepheline remains as P63 throughout the pressure range investigated, and no significant compression of the T-O bonds was measured up to 7.5 GPa. As pressure was increased to around 1 GPa the integrated intensities of the satellites decreased slightly, and at 1.8 GPa no significant intensity of the satellites was detected. Over the same pressure range the O1 site moved toward the triad and thus the tilts of the T1 and T2 tetrahedra decreased. The presence of the subsidiary non-Bragg reflections is therefore related to the split of the O1 site. When the satellites disappear at pressures above 2 GPa, the O1 site is on the triad at (2/3, 1/3, z), corresponding to a straight T1-O1-T2 bond. Below 2 GPa the structure responds to increased pressure by tilting of all four tetrahedra and above 2 GPa by tilting of the T3 and T4 tetrahedra alone. The change in compression mechanism arising from the changes in the O1 position is associated with changes in the compression of the unit-cell axes and the unit-cell volume. The volume can be described by fourth-order Birch-Murnaghan equation-of-state with parameters V0 = 723.57(4) Å3, KT0 = 47.32(26) GPa, K' = 2.77(24), and K" = 0.758(79) GPa-1. The elastic behavior along the a- and c-axis can be described with a "linearized" fourth-order Birch-Murnaghan equations-of-state, with the following refined parameters: a00 = 9.9911(2) Å, KT0(a) = 43.1(3) GPa, K'(a) = 2.5(3), and K"(a) = 0.68(8) GPa-11 for the a-axis and c0 = 8.3700(1) Å, KT0(c) = 58.6(3) GPa, K'(c) = 4.0(3), and K"(c) = 0.85(11) GPa-1 for the c-axis. The pressure-induced structural evolution in nepheline up to 7.5 GPa appears to be completely reversible. The recovery of the modulation upon complete pressure release points to the framework of nepheline having an instability corresponding to a rigid-unit mode with a wave vector corresponding to the observed positions of the satellite reflections. [ABSTRACT FROM AUTHOR]

A single crystal of orthopyroxene with composition Ca0.07Mg1.93Si2O6 (space group Pbca) has been investigated at high pressure and room temperature by in-situ X-ray diffraction using a diamond anvil cell. The unit-cell parameters have been determined at ten different pressures up to 10.16(5) GPa. In the pressure range investigated no evidences of phase transitions have been found. The pressurevolume data have been fitted with a third-order Birch-Murnaghan equation of state resulting in the following parameters: V0 = 838.26(8) ų, KT0 = 110(1) GPa, K' = 6.6(4). The Ca substitution in the pure orthoenstatite Mg2Si2O6 structure causes a slight increase in KT0 and a decrease in K'. The compressibility of a, b, and c unit-cell parameters is strongly anisotropic with a compressibility scheme βb >> βc >> βa. The structure evolution as a function of pressure has been determined at five different pressures up to 6.25(5) GPa. The M2 polyhedron undergoes the largest volume variation (∼7.7%), whereas the volume variation of M1 is ∼6.1%. The TA and TB tetrahedral volumes decrease by about 3% and 1.2%, respectively, without a discontinuity in the pressure range investigated. [ABSTRACT FROM AUTHOR]

Elastic and structural behavior of a natural cubic analcime (space group: Ia3d) from Sardinia (Italy) was investigated at high pressure by in situ single-crystal X-ray diffraction. A first-order phase transition is observed in the pressure range between 0.91(5) and 1.08(5) GPa. Unit-cell constants and reflection conditions confirm that the space group of the HP-polymorph is P1. No further phasetransition has been observed at least up to 7.14 GPa. Fitting the volume data of the cubic polymorph with a second-order BM-EoS we obtain: V0 = 2571.2(4) ų, KT0 = 56(3) GPa, and K' = 4 (fixed). For the triclinic polymorph, a third-order EoS gives: V0 = 2607(9) ų, KT0 = 19(2) GPa, and K' = 6.8(7). Axial bulk moduli of the triclinic polymorph, calculated with a linearized BM-EoS, are: KT0(a) = 29(2) GPa, with K'(a) = 4.9(6) and a0 = 13.727(10) Å; KT0(b) = 20(1) GPa, with K'(b) = 5.2(5), and b0 = 13.751(15) Å; KT0(c) = 11(1) GPa, with K'(c) = 12.6(6) and c0 = 13.822(31) Å. The elastic behavior of the HP-polymorph appears to be strongly anisotropic, being KT0(a):KT0(b):KT0(c) = 2.64:1.82:1.00. The relevant structural variations in response to the cubic → triclinic phase transition are due to tetrahedral tilting. The tetrahedral framework distortion gives rise to a change of the eight- and six-ring channels ellipticity and of the extra-framework topological configuration: it appears in fact that for the high-pressure triclinic polymorph the coordination number of some of the Na atoms is seven (2H2O + five framework O atoms) instead of six (2H2O + four framework O atoms). [ABSTRACT FROM AUTHOR]

The high-pressure behaviour and the crystal-fluid interaction of zeolites with EAB topology were investigated by in-situ single-crystal and powder synchrotron X-ray diffraction, both on synthetic and natural samples. The experiments were conducted using a diamond anvil cell and different pressure transmitting fluids, including: the non-penetrating silicone oil and the potentially penetrating methanol : ethanol : H 2 O = 16:3:1 mixture, methanol and distilled H 2 O. The zeolites intrinsic compressional behaviour investigated with a non-penetrating fluid showed the significant role of the extra framework population on the bulk compressibility. Notably, within the first ∼0.5 GPa of the silicone oil ramp, the bulk modulus (K V0 = β V0 −1) resulted to be K V0 = 62(1) GPa for the natural bellbergite and K V0 = 16(4) GPa for the synthetic K-analogue. The synthetic EAB zeolites demonstrated a high host capacity for methanol molecules, which were not able to penetrate the natural bellbergite cavities. A comparative analysis between the behaviour of zeolites with EAB topology and structurally similar zeolites, such as erionite (ERI topology) and offretite (OFF), is provided. [Display omitted] • Natural and synthetic EAB zeolites were studied under in-situ high- P conditions. • Only synthetic EABs show P -mediated intrusion of methanol molecules at few kbar. • Only a modest crystal-fluid interaction occurs in the natural sample. • Synthetic EABs are suitable for the P -induced hyper-confinement of guest molecules. [ABSTRACT FROM AUTHOR]

The high-pressure behavior of a natural erionite-K has been investigated by in situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell (DAC), using four different P -transmitting fluids: the non-penetrating silicone oil and the potentially penetrating methanol:ethanol:H 2 O = 16:3:1 mixture, pure H 2 O and naturally hydrated glycerol. The investigated crystals showed typical offretite stacking faults in the diffraction pattern. The experiment in silicone oil showed that the erionite bulk compressibility lies within the range observed for the previously investigated zeolites, as its refined bulk modulus (K V 0 = 1/ β V0), calculated within the range P amb -1.52(5) GPa, resulted equal to 47(2) GPa. The high-pressure experiments performed using potentially penetrating P -transmitting fluids showed significantly lower compressibilities, unambiguously suggesting the P -mediated intrusion of new molecules into the structural voids. Further evidence is provided by the comparative analysis of the framework deformation mechanisms: erionite-K compressed in m.e.w. showed a drastically lower compressibility of the erionite cage, with respect to silicone oil. In conclusion, this study suggests natural erionite, a relatively common zeolite, as a suitable candidate for the P -mediated intrusion and hyper-confinement of molecules into the framework microcavities. [Display omitted] • The zeolite erionite was compressed in different fluids made by diverse molecules. • In situ XRD experiments proved a selective P- induced adsorption of molecules. • Magnitude of the intrusion phenomena is surprisingly high for a natural zeolite. • Erionite is a suitable framework for the P -mediated hyper-confinement of molecules. [ABSTRACT FROM AUTHOR]