Die Mischreihe (Ca, Sr) [Al2Si2O8]

Nager, H. E.; Hoffmann, Walther G.; Nissen, H. U.

doi:10.1007/bf00601030

Cited by 13 publications

(3 citation statements)

References 3 publications

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“…The β* angle was determined from measurements on precession photographs. The following values were obtained for the direct latice and other parameters: a = 8.383 (3) These lattice constants are in agreement with the values obtained from powder spectra (BRTJNO and GAZZONI, 1969;NAGER, HOFFMANN and NISSEN, 1969).…”

Section: J !supporting

confidence: 63%

Single-crystal x-ray investigations on strontium feldspar

Bruno¹

1970

Zeitschrift Für Kristallographie - Crystalline Materials

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AuszugMit Hilfe von Einkristall-Methoden wurden an synthetischen Kristallen von Strontium-Feldspat Überstrukturreflexe vom Typ b beobachtet und damit die vermutete Gitterkonstante von 14 Ä bestätigt. Als Raumgruppe wurde 12/c bestimmt, wodurch die Annahme gestützt wird, daß der Strontium-Feldspat isostrukturell mit Celsian ist. Ein Karlsbader Zwilling wurde röntgenographisch nachgewiesen. AbstractThe crystal structure peculiarities of strontium feldspar were confirmed experimentally by a single-crystal x-ray analysis on synthetic crystals. Type b superlattice reflections were found and the length of the c parameter (14 Ä) was confirmed. The space group is I 2/c and this affirms the supposition that strontium feldspar is isostructural with celsian. A crystal twinned according to the Carlsbad law was found and examined. The complete diadochic substitution Ca-Sr and Sr-Ba, found in the aluminosilicates with formula (X,Y) [AI2S12O8] and described in several recentarticles (BRUNO and GAZZONI, 1968; BRUNO and GAZ- ZONI, 1969; NAGER, HOFFMANN and NISSEN, 1969; NAGER, BAMBATJERand HOFFMANN, 1970), made us wonder whether also the monoclinic phase SrAl2Si20s would be approximately isostructural with the calcium and barium feldspars. For the monoclinic compounds BaAl2Si20e and SrAl 2 Si 2 08, in particular, the closeness between unit-cell parameters and the strict resemblance of frequencies and intensities in the relative infrared spectra make it very likely that they are isostructural. It had still to be experimentally proved, however, that also strontium feldspar has c ~ 14 Ä. Such a value is demanded by Brought to you by | New York University Bobst Library Technical Service Authenticated Download Date | 7/15/15 10:04 PM

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Section: J !supporting

confidence: 63%

Single-crystal x-ray investigations on strontium feldspar

Bruno¹

1970

Zeitschrift Für Kristallographie - Crystalline Materials

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“…The same I1-I2/c transition can be observed with increasing temperature in Sr-rich feldspars that are triclinic at room temperature and the temperature of the transition changes with the degree of order at constant composition (Bruno and Gazzoni 1968;Nager et al 1969;Tribaudino et al 1993;McGuinn and Redfern 1997;Benna and Bruno 2003).…”

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confidence: 75%

High-pressure equation of state and phase transition in PbAl₂Si₂O₈feldspar

Curetti

Benna

Bruno

2015

American Mineralogist

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In situ high-pressure X-ray diffraction study was performed on synthetic lead feldspar with composition PbAl 2 Si 2 O 8 (PbFsp). The crystals were synthesized from the melt and thermally treated at T = 1150 °C for 12 h and at T = 1000 °C for 70 h. At room condition the unit-cell parameters are a = 8.3936(4), b = 13.0498 (7), c = 14.3258(8) Å, b = 115.281(6)°, V = 1418.9(1) Å 3 ; space group: I2/c; Q od = 0.7.A single-crystal of lead feldspar was loaded in an ETH-type diamond-anvil cell and unit-cell parameters were measured at 26 different pressures up to 8.4 GPa at room T. The evolution with P of the unit-cell parameters and volume shows a strong discontinuity between 7.7 and 8.2 GPa indicating a first-order phase transition. The discontinuous character of the transition is especially noticeable in the behavior of the b angle, which decreases from 114.83° to 114.03°, and in the b parameter, which reduces from 12.746 to 12.567 Å.In the P range 0.0001-7.72 GPa, the trend shown by the axial compressibilityis similar to that observed in the previous HP powder diffraction study, performed on lead feldspar using high-brilliance synchrotron radiation up to 7.1 GPa.In the P range 0.0001-4.27 GPa at room T, the P-V data of the I2/c lead feldspar were fitted with a second-order Birch-Murnaghan EoS. The parameters obtained are: V 0 = 1422.2(1) Å 3 and K T0 = 76.4(9) GPa. At P > 4.27 GPa, the volume values deflect from the BM2 curve and show a volume softening, precursor of the reported HP phase transition. A volume softening was recently observed in strontium feldspar (SrFsp) above 4.2 GPa.A second crystal of PbFsp was loaded in the DAC cell and in situ high-pressure X-ray diffraction intensities were measured at P = 0.0001, 2.4, 3.1, 5.4, 6.0, 7.2, 8.4, and 9.7 GPa. The appearance of c and d-type reflections at 8.4 GPa, the analysis of the systematic absence and the structural refinements indicate the HP first-order transformation as an I2/c-P2 1 /c phase transition. Structural results show that the main variations with compression in lead feldspar are in Pb-O bond lengths and in T-O-T bond angles, while T-O distances and O-T-O angles do not change meaningfully, indicating that the Si,Al tetrahedra behave with pressure as a rigid body. Changes observed in the compressional behavior of the structure between 3 and 5 GPa could explain the softening observed at P > 4 GPa in the volume compressibility.The results obtained in the present work allow comparing the pressures of the HP I2/c-P2 1 /c phase transition occurring in lead feldspar with those observed in alkaline-earth feldspars.

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“…Along the anorthite strontium feldspar join (An SrF) a complete solid solution was obtained and a I1 I2/c phase transition, due to the increase of the mean dimension of the non-tetrahedral cation, was observed (Bruno and Gazzoni, 1968;Nager, 1969;Nager et al, 1969;Bambauer and Nager, 1981;Tribaudino et al, 1993;McGuinn and Redfern, 1994;Dove and Redfern, 1997). Moreover, in the Sr-rich region of the join, samples that are triclinic at room temperature undergo an analogous I1 I2/c phase transition with increasing temperature (Bruno and Gazzoni, 1968;Nager et al, 1970;Bambauer and Nager, 1981;McGuinn and Redfern, 1997).…”

Section: Introductionmentioning

confidence: 99%

I1̄ – I2/c ferroelastic phase transition in the Ca_0.2Pb_0.8Al₂Si₂O₈ feldspar as a function of temperature

2000

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Feldspar of composition Ca0.2Pb0.8Al2Si2O8 (PbF80An20) was synthesized from melt and subsequently isothermally annealed at T = 960°C for 4 days. In situ HT X-ray powder spectra of PbF80An20 feldspar, triclinic I1̄ at room temperature, were collected in the temperature range 20–800°C, and a displacive continuous ferroelastic transition to a I2/c monoclinic phase was observed. An analysis of the symmetry-required components of the spontaneous strain tensor reveals the second order character (β = 0.46 ± 0.02) of the transition with TC = 680 ± 15°C. A linear coupling was observed between the e4 and e6 components of the spontaneous strain. The transition is analogous to those observed, with increasing temperature, along the join An–SrF and in disordered Na-rich alkali feldspars. A comparison with Ca0.2Sr0.8Al2Si2O8 feldspar (TC = 680°C, McGuinn and Redfern, 1997) shows that PbF80An20 has a higher spontaneous strain (εs = 0.028 in PbF80An20vs 0.020 in Ca0.2Sr0.8Al2Si2O8) and a higher e4 component, possibly related to the higher distortion of the non-tetrahedral polyhedron in lead feldspar.

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Die Mischreihe (Ca, Sr) [Al2Si2O8]

Cited by 13 publications

References 3 publications

Single-crystal x-ray investigations on strontium feldspar

Single-crystal x-ray investigations on strontium feldspar

High-pressure equation of state and phase transition in PbAl₂Si₂O₈feldspar

I1̄ – I2/c ferroelastic phase transition in the Ca_0.2Pb_0.8Al₂Si₂O₈ feldspar as a function of temperature

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Die Mischreihe (Ca, Sr) [Al2Si2O8]

Cited by 13 publications

References 3 publications

Single-crystal x-ray investigations on strontium feldspar

Single-crystal x-ray investigations on strontium feldspar

High-pressure equation of state and phase transition in PbAl2Si2O8feldspar

I1̄ – I2/c ferroelastic phase transition in the Ca0.2Pb0.8Al2Si2O8 feldspar as a function of temperature

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High-pressure equation of state and phase transition in PbAl₂Si₂O₈feldspar

I1̄ – I2/c ferroelastic phase transition in the Ca_0.2Pb_0.8Al₂Si₂O₈ feldspar as a function of temperature