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The thermoelastic behavior and structural evolution of a natural balliranoite (Na 4.47 Ca 2.86 K 0.11 )(Si 5.96 Al 6.04 O 24 )Cl 2.03 (CO 3 ) 0.78 (SO 4 ) 0.33 , a = 12.6701(3) A, c = 5.3178(1) A and V = 739.30(3) A 3 , space group P 6 3 , the CO 3 2 - analogue of davyne, a cancrinite-group mineral, have been studied within the range 108 ⩽ T (K) ⩽ 293 by in situ single-crystal X-ray diffraction. No evidences of phase transition or change of the “compressional” behavior have been observed. The refined volume thermal expansion coefficient is α V = 4.6(4) ∗ 10 −5 K −1 , whereas the refined unit-cell edges linear thermal expansion coefficients are α a = 1.4(2) ∗ 10 −5 K −1 and α c = 1.7(2) ∗ 10 −5 K −1 . The structural evolution at T ⩽ 293 K is driven by the rotation of the rigid TO 4 framework tetrahedra. A description of the main deformation mechanisms is carried out along with a comparison with the cancrinite behavior at the same temperature conditions. Significant differences pertaining to the mechanisms acting on the (0 0 0 1) plane are observed between these isotypic materials. These results suggest that the coordination environment of cations within the can unit could influence the magnitude of the [CAN] framework deformation at low- T .

The thermo-elastic behavior and the P/T- induced structure evolution of a synthetic CsAlSiO 4 [ABW framework type, with Pc 2 1 n space group and lattice parameters: a = 9.414(1), b = 5.435(1), c = 8.875(1) A at room conditions] have been investigated up to 1000 °C (at 0.0001 GPa) and up to 10 GPa (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) A 3 , K T0 = 42(1) GPa and K ′ = 3.9(3) (with a second-order Birch–Murnaghan Equation of State: V 0 = 458.1(2) A 3 , 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 [1 0 0] and [0 1 0] at P > 4 GPa. 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 + α 0 · T + α 1 · 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 [1 0 0] (i.e. α 0 ( a ) = −9.97(1) × 10 −6 °C −1 ), almost no expansion along [0 1 0] (i.e. α 0 ( b ) = 0.36(1) × 10 −6 °C −1 ) and a pronounced positive expansion along [0 0 1] (i.e. α 0 ( c ) = 47.46(6) × 10 −6 °C −1 ). The main P/T -induced structure deformation mechanisms, at the atomic level, are discussed.

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 4.3 GPa. 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 1.1–1.3 GPa and the second at 2.7–3.2 GPa. 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 3.2–4.3 GPa), giving the following isothermal bulk moduli ( K V 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 [1 0 0] undergoes a significant increase of ellipticity, whereas the channel parallel to [0 1 0] undergoes a shrinking towards a circular shape at P ≥ 1.3 GPa. A partial re-organization of the H 2 O sites occurs between 1.1 and 1.3 GPa, and new framework deformational modes onset at P ≥ 3.2 GPa, coupled with a change in the coordination environment of the extraframework cations.

The low-temperature structural behaviour of natural cancrinite with a formula Na6.59Ca0.93[Si6.12Al5.88O24](CO3)1.04F0.41·2H2O has been investigated by means of in situ single-crystal X-ray diffraction and Raman spectroscopy. High quality structure refinements were obtained at 293, 250, 220, 180, 140, 100 and at 293 K again (at the end of the low-T experiments). The variation in the unit-cell volume as a function of temperature (T) exhibits a continuous trend, without any evident thermoelastic anomaly. The thermal expansion coefficient αV = (1/V)∂V/∂T is 3.8(7) × 10–5 K–1 (between 100 and 293 K). The structure refinement based on intensity data collected at ambient conditions after the low-T experiment confirmed that the low-T induced deformation processes are completely reversible. The extraframework population does not show significant variations down to 100 K. The strong positional disorder of the carbonate groups along the c axis persists within the T range investigated. The structural behaviour of cancrinite at low-T is mainly governed by the continuous framework rearrangement through the ditrigonalization of the six-membered rings which lie in a plane perpendicular to [0001], the contraction of the four-membered ring joint units, the decrease of the ring corrugation in the (0001) plane, and the flattening of the cancrinite cages. A list of the principal Raman active modes in ambient conditions is provided and discussed.

The crystal structure, crystal chemistry and low-temperature (L T ) behavior of a natural gobbinsite [(Na 4.97 K 0.07 Ca 0.48 ) Σ5.52 [Al 5.62 Si 10.29 ] Σ15.91 O 32 ·11.9H 2 O, Z = 1, a = 10.1185(4), b = 9.8035 (4), c = 10.1692(4) A and V = 1008.75(10) A 3 , space group Pmnb ] have been studied by in situ L T single-crystal X-ray diffraction. Five structural refinements were conducted on the basis of intensity data collected at 293 (room conditions), 250, 200, 150 and 100 K. Reflection conditions confirmed that the space group Pmnb is maintained within the T -range investigated. At room temperature, the same extra-framework population described by Gatta et al. [7] was found, with one site partially occupied by Na, one site partially occupied by Ca, and five sites partially occupied by water. At low- T a partial dehydration, likely induced by the N 2 -flow, was observed, with a significant rearrangement of the extra-framework configuration. Low- T induced deformations of the 8- and 4-membered rings were observed, and the relationships between the main deformation mechanisms of the tetrahedral framework and the contraction along the unit-cell edges are discussed.

The high-pressure behavior of a synthetic siliceous ferrierite has been studied by in situ single-crystal and powder synchrotron X-ray diffraction with a diamond anvil cell, using four different P-transmitting fluids: the non-penetrating silicone oil and the potentially pore-penetrating methanol:ethanol:H2O = 16:3:1 mixture, ethylene glycol and 2methyl-2propen-1ol. The high-pressure experiment in silicone oil shows a remarkable flexibility of the FER framework. Two displacive phase transitions, following the path Pmnn-to-P121/n1-to-P21/n11 with pressure, were observed. The three polymorphs were found to share a virtually identical bulk compressibility, though showing a different anisotropic pattern. The experiments with potentially penetrating media enhanced the occurrence of a complex scenario, from which the P-induced intrusion of fluid molecules into the FER structural voids can be assumed by the different phase-transition paths and compressibility patterns, by the calculated residual electron density and by the different deformation mechanisms at the atomic scale, observed as a function of the used medium. The starting orthorhombic polymorph was always restored upon decompression in all the experiments. The roles of the different surface area in single crystal and polycrystalline samples, and of the process kinetics on the compressibility and crystal–fluid interactions, are discussed.

The compressional behaviour of (triclinic) pyrophyllite-1Tc was investigated by means of in situ synchrotron single-crystal diffraction up to 6.2 GPa (at room temperature) using a diamond anvil cell. Its thermal behaviour was investigated by in situ synchrotron powder diffraction up to 923 K (at room pressure) with a furnace. No evidence of phase transition has been observed within the pressure range investigated. The α angle decreases whereas the β and γ angles increase with P, with the following linear trends: α(P) = α 0 − 0.203(9)·ΔP, β(P) = β 0 + 0.126(8)·ΔP, and γ(P) = γ 0 + 0.109(5)·ΔP (angles in ° and P in GPa). P–V data fits with isothermal Murnaghan and third-order Birch-Murnaghan Equations of State yield: K T0 = 47(3) GPa and K′ = 6.6(14) for the M-EoS fit, K T0 = 47(4) GPa and K′ = 7.3(19) for a III-BM-EoS fit, with the following anisotropic compressional scheme: β a :β b :β c = 1.06:1:4.00. The evolution of the “Eulerian finite strain” versus “normalized stress” leads to: Fe(0) = 47(3) GPa as intercept value and regression line slope with K′ = 7.1(18). A drastic and irreversible change of the thermal behaviour of pyrophyllite-1Tc was observed at 700 1,123 K, an irreversible transformation occurs, likely ascribable to the first stage of the T-induced de-hydroxylation. Between 423 and 1,123 K, the β angle decreases in response to the applied temperature; all the unit-cell edges show a monotonic increase. The volume expansion coefficient of talc was modelled between 423 and 1,123 K by the linear regression, yielding: V(T)/V 0 = 1 + α 0V·T = 1 + 2.15(3) × 10−5 (T − T 0). The comparative elastic analysis of pyrophyllite and talc, using the data obtained in this and in previous studies, shows that pyrophyllite is more compressible and more expandable than talc.

Black phosphorous (BP) is one of the important emerging two-dimensional systems. We have undertaken a structural investigation of BP in the temperature range of 320 K to 85 K using synchrotron X-ray diffraction (XRD) studies. The XRD pattern of BP is heavily influenced by the preferred orientation effects. Collection of the diffraction pattern in a standard capillary geometry with controlled capillary rotations perpendicular to the X-ray direction permitted us to provide insights to the effects of the preferred orientation. In the range of 320 K to 85 K, BP remains in the so-called “A17” orthorhombic structure. Lattice parameters show a regular shrinkage with the lowering of the temperature as expected for any elemental metallic system. Dense temperature sampling permitted us to observe a small but clear deviation from the linear behavior in of one of the in-plane lattice parameters. This temperature-dependent structural evolution seems to provide some insights into the temperature dependence of the macroscopic properties of BP such as the Hall coefficient, thermal conductivity, etc.

In the present paper it is described an analysis procedure suited for experiments where cross-sections strongly varying with energy are measured using beams having large energy dispersion. These cross-sections are typically the sub-barrier fusion excitation function of reactions induced by radioactive beams. The large beam energy dispersion, typical of these experiments, can lead to ambiguities in the association of the effective beam energy to the reaction product yields and consequently to an error in the determination of the excitation function. As a test case, the approach is applied to the experiments 6 Li+120 Sn and 7 Li+119 Sn measured in the energy range 14 MeV ≤ Ec.m. ≤28 MeV. The complete fusion cross sections are deduced from activation measurements using the stacked target technique. The results of these experiments, that employ the two weakly-bound stable Li isotopes, show that the complete fusion cross sections above the barrier are suppressed of about 70% and 85% with respect to the Universal Fusion Function, used as a standard reference, in the 6 Li and 7 Li induced reactions respectively. Moreover, the excitation functions of the two systems at energies below the barrier, do not show significant differences, despite the two systems have different n -transfer Qvalue .

The high-temperature thermoelastic behavior of a natural cancrinite has been investigated by in situ single-crystal X-ray diffraction. The unit-cell volume variation as a function of temperature (T) exhibits a continuous trend up to 748 K (hydrous expansion regime). The unit-cell edges expansion clearly shows an anisotropic expansion scheme (α a

The P/T phase stability and the thermo-elastic behavior of synthetic TlAlSiO 4 [ABW framework type, space group Pna 2 1 , a = 8.2719(2), b = 9.4373(2), c = 5.4180(1) A] have been investigated up to 950 °C (at room- P ) and up to 8 GPa (at room- T ) by means of in situ synchrotron powder diffraction with a diamond anvil cell and with a high-temperature furnace. The Rietveld structure refinement of TlAlSiO 4 at room P/T confirms the general structure model previously reported. Only one independent Tl site, with full site occupancy and close to channel wall, represents the extra-framework population. No phase transition has been observed within the temperature- and pressure-range investigated. P – V data were fitted to a second-order Birch–Murnaghan Equation of State (BM-EoS), giving: V 0 = 420.76(5) A 3 , K T0 = 48.8(2) GPa. The evolution of the lattice parameters with pressure shows a significantly anisotropic compressional pattern. The elastic parameters calculated with a “linearized” second-order BM-EoS are: K T0 ( a ) = 21.96(7) GPa for the a -axis; K T0 ( b ) = 68(1) GPa for the b -axis, and K T0 ( c ) = 112(2) GPa for the c -axis. The volume thermal expansion with T was modeled by the polynomial function: V ( T )/ V 0 = 1 + α 0 ·Δ T + α 1 ·Δ T 2 = 1 + 4.44(3)·10 −5 ·Δ T − 2.3(3)·10 −9 ·Δ T 2 . The anisotropic thermal scheme is characterized by a negative thermal expansion along [010] (i.e. α 0 ( b ) = −8.5(1)·10 − 6 °C −1 ), almost no expansion along [0 0 1] (i.e. α 0 ( c ) = 0.9(1)·10 − 6 °C −1 ) and a positive expansion along [1 0 0] (i.e. α 0 ( a ) = 52.4(1)·10 − 6 °C −1 ). A comparative analysis of the thermo-elastic behavior of the isotypic TlAlSiO 4 and CsAlSiO 4 is carried out.

Journal of the American Ceramic Society 96(8), 2583 - 2592 (2013). doi:10.1111/jace.12411, Published by Wiley-Blackwell, Oxford [u.a.]

The thermo-elastic behaviour of Be2BO3(OH)0.96F0.04 (i.e. natural hambergite, Z = 8, a = 9.7564(1), b = 12.1980(2), c = 4.4300(1) A, V = 527.21(1) A3, space group Pbca) has been investigated up to 7 GPa (at 298 K) and up to 1,100 K (at 0.0001 GPa) by means of in situ single-crystal X-ray diffraction and synchrotron powder diffraction, respectively. No phase transition or anomalous elastic behaviour has been observed within the pressure range investigated. P−V data fitted to a third-order Birch–Murnaghan equation of state give: V 0 = 528.89(4) A3, K T0 = 67.0(4) GPa and K′ = 5.4(1). The evolution of the lattice parameters with pressure is significantly anisotropic, being: K T0(a):K T0(b):K T0(c) = 1:1.13:3.67. The high-temperature experiment shows evidence of structure breakdown at T > 973 K, with a significant increase in the full-width-at-half-maximum of all the Bragg peaks and an anomalous increase in the background of the diffraction pattern. The diffraction pattern was indexable up to 1,098 K. No new crystalline phase was observed up to 1,270 K. The diffraction data collected at room-T after the high-temperature experiment showed that the crystallinity was irreversibly compromised. The evolution of axial and volume thermal expansion coefficient, α, with T was described by the polynomial function: α(T) = α 0 + α 1 T −1/2. The refined parameters for Be2BO3(OH)0.96F0.04 are: α 0 = 7.1(1) × 10−5 K−1 and α 1 = −8.9(2) × 10−4 K −1/2 for the unit-cell volume, α 0(a) = 1.52(9) × 10−5 K−1 and α 1(a) = −1.4(2) × 10−4 K −1/2 for the a-axis, α 0(b) = 4.4(1) × 10−5 K−1 and α 1(b) = −5.9(3) × 10−4 K −1/2 for the b-axis, α 0(c) = 1.07(8) × 10−5 K−1 and α 1(c) = −1.5(2) × 10−4 K −1/2 for the c-axis. The thermo-elastic anisotropy can be described, at a first approximation, by α 0(a):α 0(b):α 0(c) = 1.42:4.11:1. The main deformation mechanisms in response to the applied temperature, based on Rietveld structure refinement, are discussed.

The structural evolution at high pressure of a natural 2M 1-phengite [(K0.98Na0.02)Σ=1.00(Al1.55Mg0.24Fe0.21Ti0.02)Σ=2.01(Si3.38Al0.62)O10(OH)2; a = 5.228(2), b = 9.057(3), c = 19.971(6)A, 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 T0 = 57.3(10) GPa and K′ = ∂K T0/∂P = 6.97(24). The single-crystal structure refinements showed that the significant elastic anisotropy of the 2M 1-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 T0(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 T0 = 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 2M 1- and 3T-phengite is discussed.

The high-pressure structural evolution of a natural 3T-phengite [(K0.90Na0.05)S = 0.95(Al1.51Mg0.32Fe0.18Ti0.03)S = 2.04(Si3.40Al0.60)O10(OH)2, a = b = 5.2279(11) and c = 29.752(7) Å, space group: P3112] from 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 about 10 GPa. Nine structural refinements were performed at selected pressures within the P-range investigated. The compressional behavior of the same phengite sample was previously studied up to about 27 GPa by synchrotron X-ray powder diffraction, and the corresponding P–V curve was modeled by a third-order Birch–Murnaghan Equation of State (BM-EoS). The significant elastic anisotropy of the 3T-phengite (i.e. β(c) > β(a)) is mainly controlled by the compression of the K-polyhedra. The evolution of the volume of the inter-layer K-polyhedron as a function of P is monotonic, without any evidence of discontinuity. Fitting the P–V data with a truncated second-order BM-EoS, we obtain a bulk modulus value of K 0(K-polyhedron) = 35(3) GPa. The tetrahedra and octahedra in the 3T-phengite structure are significantly less compressible than the K-polyhedron, and behave similarly to rigid units within the P-range investigated. The main P-induced effect on the tetrahedral sheet consists in a cooperative rotation of the tetrahedra, describable by the evolution of the “tetrahedral rotation angle” (or “ditrigonal rotation angle”, α) as a function of P. The value of the ditrigonal rotation angle increases significantly with P: α (°) = α P0 + 0.57(2)P (GPa) [R about 99%]. The volume of the K-polyhedron and the value of ditrigonal rotation parameter (α) are not independent of one another, showing a correlation of about 99%.

In-situ investigations on BaMg(CO3)2 (= α-phase, space group R-3c) by means of single-crystal diffraction and Raman spectroscopy yield the existence of novel structural polymorphs at high-pressure (γ-phase, C2/c) and high-temperature (β-phase, R-3m) conditions. Isothermal hydrostatic compression at room temperature yield a high-pressure phase transition at Pc ≍ 2.3210.04 GPa, which is weakly first order in character and reveals significant elastic softening of the high-pressure form (α: K0 = 66.212.3 GPa, dK/dP = 2.011.8; γ: K0 = 41.910.4 GPa, dK/dP = 6.110.3). X-ray structure determination confirms a distorted but topologically similar crystal structure of the γ-phase, with Ba in twelve-fold and Mg in octahedral coordination together with characteristic CO3 units. Based on the experimental series of in-situ HPHT data points, the phase boundary of the α-to-γ-transition was determined with a Clausius-Clapeyron slope of 9.8(7) × 10-3 GPa K-1. In-situ measurements of the X-ray intensities carried out to identify the nature of the structural variation correspond to the previously reported transformation from α- to β-BaMg(CO3)2 at 343 K and 1 bar. The investigations revealed, in contrast to all X-ray diffraction data recorded at 298 K, the disappearance of the superstructure reflections and the observed reflection conditions confirm the anticipated R-3m space-group symmetry. The pathway of structural transformation follows a typically displacive fashion, involving exclusively positional shifts of the oxygen atoms for the α-β-transformation. In contrast, in the atomic displacement of the Ba atoms in addition to the three crystallographically independent oxygen sites is responsible for a comparably higher flexibility of the C2/c structure, which explains the origin of the remarkable elastic softening.