High-pressure polymorphism and structural transitions of norsethite, BaMg(CO3)2

Pippinger, Thomas; Miletich, Ronald; Effenberger, H.; Hofer, Gregor; Lotti, Paolo; Merlini, Marco

doi:10.1007/s00269-014-0687-8

Cited by 14 publications

(19 citation statements)

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“…Various approaches for structure refinements (in models of R3c, R3, R3c, R3m and R32 symmetry, including atomic order and disorder and allowing displacements of the O atoms from supposed mirror planes) clearly proved the R3c structure model with a c 0 = 2c superstructure, as verified by specified positions at fully occupied Wyckoff sites and inconspicuous displacement parameters (Effenberger et al, 2014). Moreover, in situ investigations under conditions of variable pressure (P) and temperature (T) revealed transformations into high-T -BaMg(CO 3 ) 2 (R3m) and high-P -BaMg(CO 3 ) 2 (C2/c) phases (Pippinger et al, 2014;Effenberger et al, 2014). While the high-pressure studies also provided structural insight into the mechanism of the pressure-driven (R3c)-to-(C2/c) transitions, the T-dependent investigations were performed mainly by means of IR and Raman spectroscopy, in addition to XRD and thermal measurements on powder samples.…”

Section: Introductionmentioning

confidence: 77%

Evolution of the α-BaMg(CO₃)₂low-temperature superstructure and the tricritical nature of its α–β phase transition

Ende

Effenberger

Miletich

2017

Acta Crystallogr Sect B

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The crystal structure of the synthetic double carbonate norsethite [BaMg(CO)] has been reinvestigated using X-ray diffraction data within the temperature range 100-500 K using a high-sensitivity PILATUS pixel detector. The previously assumed positional shift of the crystallographically unique oxygen atom is confirmed. The shift is associated with a coupled rotation of symmetry-equivalent carbonate groups. It was possible to follow the shift using high-accuracy experiments under varying temperature conditions between 100 K and the critical transition temperature occurring at T = 363 ± 3 K. The transition of the α-form (space group R{\bar 3}c; below T), which represents a superstructure of the β-form (space group R{\bar 3}m, with c' = c/2; above T) was studied in detail. The tricritical order character of this displacive phase transition was verified by tracking the intensities of the recorded superstructure reflections (l = 2n + 1) from single-crystal diffraction and using high-precision lattice parameters obtained from powder diffraction in transmission geometry. Thermodynamic properties suggest both rotation of the CO group and a coordination change of the BaO coordination polyhedra as the order parameters driving the temperature-dependent α-β phase transition. Nevertheless, a detailed structural analysis reveals the coordination change of the barium atoms to be the main driving force for the observed transformation.

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Section: Introductionmentioning

confidence: 77%

Evolution of the α-BaMg(CO₃)₂low-temperature superstructure and the tricritical nature of its α–β phase transition

Ende

Effenberger

Miletich

2017

Acta Crystallogr Sect B

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“…Pressures were determined from ruby and Sm 2+ -doped SrB 4 O 7 optical pressure sensors. High-pressure high-temperature (HPHT) measurements were taken in analogy to Pippinger et al (2014) by applying the composite-gasket technique (Miletich et al 2009). The experimental pressure and temperature conditions were determined from the luminescence signals of ruby and Sm 2+ -doped SrB 4 O 7 sensors following the method of Datchi et al (2007).…”

Section: Sample Materialsmentioning

confidence: 99%

Puzzling calcite-III dimorphism: crystallography, high-pressure behavior, and pathway of single-crystal transitions

et al. 2014

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at temperatures up to 550 K. High-pressure raman spectra reveal distinguishable characteristic spectral differences located in the wave number range of external modes with the occurrence of band splitting and shoulders due to subtle symmetry changes. Constraints from in situ observations suggest a stability field of CaCO 3 -IIIb at relatively low temperatures adjacent to the calcite-II field. Isothermal compression of calcite provides the sequence from I to II, IIIb, and finally, III, with all transformations showing volume discontinuities. re-transformation at decreasing pressure from III oversteps the stability field of IIIb and demonstrates the pathway of pressure changes to determine the transition sequence. Clausius-Clapeyron slopes of the phase boundary lines were determined as: ΔP/ΔT = −2.79 ± 0. 28 × 10 −3 gPa K −1 (I-II); +1.87 ± 0.31 × 10 −3 gPa K −1 (II/III); +4.01 ± 0.5 × 10 −3 gPa K −1 (II/IIIb); −33.9 ± 0.4 × 10 −3 gPa K −1 (IIIb/III). The triple point between phases II, IIIb, and III was determined by intersection and is located at 2.01(7) gPa/338(5) K. The pathway of transition from I over II to IIIb can be interpreted by displacement with small shear involved (by 2.9° on I/II and by 8.2° on II/IIIb). The former triad of calcite-I corresponds to the [20-1] direction in the P2 1 /c unit cell of phase II and to [101] in the pseudomonoclinic C1 setting of phase IIIb. Crystal structure investigations of triclinic CaCO 3 -III at non-ambient pressure-temperature conditions confirm the reported structure, and the small changes associated with the variation in P and T explain the broad stability of this structure with respect to variations in P and T. PVT equation of state parameters was determined from experimental data points in the range of 2.20-6.50 gPa at 298-405 K providing K T 0 = 87.5(5.1) gPa, (δK T /δT) P = −0.21(0.23) gPa K −1 , α 0 = 0.8(21.4) × 10 −5 K −1 , and α 1 = 1.0(3.7) × 10 −7 K −1 using a second-order Birch-Murnaghan equation of state formalism.Abstract High-pressure phase transformations between the polymorphic forms I, II, III, and IIIb of CaCO 3 were investigated by analytical in situ high-pressure high-temperature experiments on oriented single-crystal samples. all experiments at non-ambient conditions were carried out by means of raman scattering, X-ray, and synchrotron diffraction techniques using diamond-anvil cells in the pressure range up to 6.5 gPa. The composite-gasket resistive heating technique was applied for all high-pressure investigations T. Yagi is on sabbatical leave at

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“…A six-fold coordination seems to be unusual; for instance in the other known anhydrous barium double carbonate mineral, norsethite, BaMg(CO 3 ) 2 , Ba is twelve-fold coordinated with an average <Ba–O> distance of 2.947 Å (Effenberger and Zemann, 1985), although recent structural investigations suggested a [6+6] coordination for norsethite and its Mn-analogue BaMn(CO 3 ) 2 (e.g. Effenberger et al ., 2014; Pippinger et al ., 2014; Wen et al ., 2019). In witherite, BaCO 3 , Ba is nine-fold coordinated (e.g.…”

Section: Crystal Structure Of Alstonitementioning

confidence: 99%

The crystal structure of alstonite, BaCa(CO₃)₂: an extraordinary example of ‘hidden’ complex twinning in large single crystals

Bindi

Roberts

Biagioni

2020

MinMag

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Alstonite, BaCa(CO3)2, is a mineral described almost two centuries ago. It is widespread in Nature and forms magnificent cm-sized crystals. Notwithstanding, its crystal structure was still unknown. Here, we report the crystal-structure determination of the mineral and discuss it in relationship to other polymorphs of BaCa(CO3)2. Alstonite is trigonal, space group P31m, with unit-cell parameters a = 17.4360(6), c = 6.1295(2) Å, V = 1613.80(9) Å3 and Z = 12. The crystal structure was solved and refined to R1 = 0.0727 on the basis of 4515 reflections with Fo > 4σ(Fo) and 195 refined parameters. Alstonite is formed by the alternation, along c, of Ba-dominant and Ca-dominant layers, separated by CO3 groups parallel to {0001}. The main take-home message is to show that not all structure determinations of minerals/compounds can be solved routinely. Some crystals, even large ones displaying excellent diffraction quality, can be twinned in complex ways, thus making their study a crystallographic challenge.

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High-pressure polymorphism and structural transitions of norsethite, BaMg(CO3)2

Cited by 14 publications

References 42 publications

Evolution of the α-BaMg(CO₃)₂low-temperature superstructure and the tricritical nature of its α–β phase transition

Evolution of the α-BaMg(CO₃)₂low-temperature superstructure and the tricritical nature of its α–β phase transition

Puzzling calcite-III dimorphism: crystallography, high-pressure behavior, and pathway of single-crystal transitions

The crystal structure of alstonite, BaCa(CO₃)₂: an extraordinary example of ‘hidden’ complex twinning in large single crystals

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High-pressure polymorphism and structural transitions of norsethite, BaMg(CO3)2

Cited by 14 publications

References 42 publications

Evolution of the α-BaMg(CO3)2low-temperature superstructure and the tricritical nature of its α–β phase transition

Evolution of the α-BaMg(CO3)2low-temperature superstructure and the tricritical nature of its α–β phase transition

Puzzling calcite-III dimorphism: crystallography, high-pressure behavior, and pathway of single-crystal transitions

The crystal structure of alstonite, BaCa(CO3)2: an extraordinary example of ‘hidden’ complex twinning in large single crystals

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Product

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Evolution of the α-BaMg(CO₃)₂low-temperature superstructure and the tricritical nature of its α–β phase transition

Evolution of the α-BaMg(CO₃)₂low-temperature superstructure and the tricritical nature of its α–β phase transition

The crystal structure of alstonite, BaCa(CO₃)₂: an extraordinary example of ‘hidden’ complex twinning in large single crystals