High-pressure Crystal Chemistry Research Articles

Mapping high-pressure crystallography in a structural chemistry landscape

The remarkable growth in volume of high-pressure crystal structural chemistry depositions in the Cambridge Structure Database has been reported in a recent paper by Kaźmierczak & Patyk-Kaźmierczak [Acta Cryst. (2021), B77, 1012–1020].

Lab in a DAC - high-pressure crystal chemistry in a diamond-anvil cell.

The diamond-anvil cell (DAC) was invented 60 years ago, ushering in a new era for material sciences, extending research into the dimension of pressure. Most structural determinations and chemical research have been conducted at ambient pressure, i.e. the atmospheric pressure on Earth. However, modern experimental techniques are capable of generating pressure and temperature higher than those at the centre of Earth. Such extreme conditions can be used for obtaining unprecedented chemical compounds, but, most importantly, all fundamental phenomena can be viewed and understood from a broader perspective. This knowledge, in turn, is necessary for designing new generations of materials and applications, for example in the pharmaceutical industry or for obtaining super-hard materials. The high-pressure chambers in the DAC are already used for a considerable variety of experiments, such as chemical reactions, crystallizations, measurements of electric, dielectric and magnetic properties, transformations of biological materials as well as experiments on living tissue. Undoubtedly, more applications involving elevated pressure will follow. High-pressure methods become increasingly attractive, because they can reduce the sample volume and compress the intermolecular contacts to values unattainable by other methods, many times stronger than at low temperature. The compressed materials reveal new information about intermolecular interactions and new phases of single- and multi-component compounds can be obtained. At the same time, high-pressure techniques, and particularly those of X-ray diffraction using the DAC, have been considerably improved and many innovative developments implemented. Increasingly more equipment of in-house laboratories, as well as the instrumentation of beamlines at synchrotrons and thermal neutron sources are dedicated to high-pressure research.

Pressure-induced dehydration of dioptase: A single-crystal X-ray diffraction and Raman spectroscopy study

We present a synchrotron-based, single-crystal X-ray diffraction and Raman spectroscopy study of natural green dioptase (Cu6Si6O18·6H2O) up to ∼30GPa at room temperature. The lattice parameters of dioptase exhibit continuous compression behavior up to ∼14.5GPa, whereupon a structural transition is observed. Pressure–volume data below 14.5GPa were fitted to a second-order Birch–Murnaghan equation of state with V0=1440(2) Å3 and K0=107(2) GPa, with K0′=4(fixed). The low-pressure form of dioptase exhibits anisotropic compression with axial compressibility βa>βc in a ratio of 1.14:1.00. Based on the diffraction data and Raman spectroscopy, the new high-pressure phase could be regarded as a dehydrated form of dioptase in the same symmetry group. Pressure-induced dehydration of dioptase contributes broadly to our understanding of the high-pressure crystal chemistry of hydrous silicates containing molecular water groups.

The high-pressure behavior of spherocobaltite (CoCO3): a single crystal Raman spectroscopy and XRD study

Magnesite (MgCO3), calcite (CaCO3), dolomite [(Ca, Mg)CO3], and siderite (FeCO3) are among the best-studied carbonate minerals at high pressures and temperatures. Although they all exhibit the calcite-type structure ( $${\text{R}}\bar{3}{\text{c}}$$ ) at ambient conditions, they display very different behavior at mantle pressures. To broaden the knowledge of the high-pressure crystal chemistry of carbonates, we studied spherocobaltite (CoCO3), which contains Co2+ with cation radius in between those of Ca2+ and Mg2+ in calcite and magnesite, respectively. We synthesized single crystals of pure spherocobaltite and studied them using Raman spectroscopy and X-ray diffraction in diamond anvil cells at pressures to over 55 GPa. Based on single crystal diffraction data, we found that the bulk modulus of spherocobaltite is 128 (2) GPa and K′ = 4.28 (17). CoCO3 is stable in the calcite-type structure up to at least 56 GPa and 1200 K. At 57 GPa and after laser heating above 2000 K, CoCO3 partially decomposes and forms CoO. In comparison to previously studied carbonates, our results suggest that at lower mantle conditions carbonates can be stable in the calcite-type structure if the radius of the incorporated cation(s) is equal or smaller than that of Co2+ (i.e., 0.745 A).

Variable temperature and high-pressure crystal chemistry of perovskite formamidinium lead iodide: a single crystal X-ray diffraction and computational study.

We investigate the variable temperature (100-450 K) and high-pressure (p = ambient - 0.74 GPa) crystal chemistry of the black perovskite formamidinium lead iodide, [(NH2)2CH]PbI3, using single crystal X-ray diffraction. In both cases we find a phase transition to a tetragonal phase. Our experimental results are combined with first principles calculations, providing information about the electronic properties of [(NH2)2CH]PbI3 as well as the most probable orientation of the [(NH2)2CH]+ cations.

Multicomponent A-site ordered perovskite BiMn3(Fe0.25Ti0.75)4O12: High-pressure synthesis, crystal chemistry and magnetic behavior

Abstract A new multicomponent A-site ordered perovskite-type oxide has been successfully synthesized in the BiFeO 3 and MnTiO 3 pseudobinary system at high pressure and temperature, 6 GPa and 1300 K. It is found that the oxide is an A-site ordered and B-site disordered perovskite Bi 3+ Mn 2+ 3 (Fe 3+ 0.25 Ti 4+ 0.75 ) 4 O 12 in the space group of the cubic high symmetry Im -3 with a lattice parameter a =7.5937(3) A. It should be noted that the Mn 2+ ions in the A ′-site show a site-splitting, while the Bi 3+ ones are in a regular icosahedron position of the A -site. On the other hand, the Fe 3+ and Ti 4+ ones in the B -site are disordered in this perovskite structure. The temperature dependence of magnetizations and specific heats at low temperatures shows spin-glass-like behaviors below 11 K.

High-pressure stability and ambient metastability of marcasite-type rhodium pernitride

High-pressure stability, ambient metastability, and high-pressure crystal chemistry of chemical bonds of marcasite-type RhN2 have been investigated using a laser-heated diamond-anvil cell up to a pressure of 70.6 GPa. High-pressure in-situ X-ray diffraction and Raman scattering measurements revealed that the marcasite-type RhN2 structure is stable up to 70.6 GPa and exhibited an order of axial compressibility of βc > βb > βa. This indicates that single bonded nitrogen dimer (N-N) plays an important role in the incompressibility of a- and b-axes than in that of the c-axis and stabilizes the marcasite-type structure at high-pressure. Field emission scanning electron microscopic analysis in combination with the energy dispersive X-ray spectroscopic measurements and the result of our previous study indicates that the marcasite-type RhN2 can be quenched to ambient pressure when the grain size is less than 100 nm. Our study together with other previous studies indicates that the ambient metastability of 4d platinum group pernitrides (RuN2, RhN2, and PdN2) decreases from ruthenium to palladium.

High-pressure crystal chemistry of coesite-I and its transition to coesite-II

Abstract The high-pressure crystal chemistry of coesite was studied by means of single crystal X-ray diffraction in the pressure interval ∼2–34 GPa and at ambient temperature. We compressed the samples using diamond-anvil cells loaded with neon as pressure-transmitting medium and collected X-ray diffraction data using synchrotron radiation. The thermodynamically stable coesite – coesite-I – was observed up to ∼20 GPa, with the following unit-cell parameters: a = 6.6533(12) Å, b = 11.9018(10) Å, c = 6.9336(10) Å, β = 121.250(20)° and V = 469.38(15) Å3. The volume-pressure data of coesite-I are described by means of a third-order Birch-Murnhagan EoS with parameters V 0 = 547.26(66) Å3, K T0 = 96(4) GPa, K ′ T o ${K'_{To}}$ = 4.1(4). Above such pressure we witness the formation of a well crystallized coesite-II, previously observed only by spectroscopic studies. The structure of the novel high-P polymorph was determined and refined at ∼28 and ∼31 GPa with final R indices of 8% and 12%, respectively. Coesite-II has P21/n symmetry and a unit cell that is “doubled” along the b-axis with respect to that of the initial coesite-I: a = 6.5591(10) Å, b = 23.2276(14) Å, c = 6.7953(9) Å, β = 121.062(19)° and V = 886.84(19) Å3 at ∼28 GPa. All Si atoms are in tetrahedral coordination. The displacive phase transition I->II is likely driven by the extreme shortening (0.05 Å or 3.2%) of the shortest and the most compressible Si1-O1 bond, related to the stiff 180° Si1-O1-Si1 angle. Under compression the linear angle bends, resulting in two independent angles, one of which, however, retains almost linear geometry (∼178°). The requirement of this angle to be close to linear likely causes further Si-O compression down to an extremely short distance of ∼1.52 Å which prompts subsequent structural changes, with the formation of a triclinic phase at ∼31 GPa, coesite-III.

Evidence of a long C-C attractive interaction in cerussite mineral: QTAIM and ELF analyses.

Cerussite, an orthorhombic lead carbonate mineral, has a structure and physical properties that cannot be understood merely in terms of ionic anion-cation interactions. The nature of the chemical bonding in cerussite is analyzed by means of the quantum theory of atoms in molecules (QTAIM) and the analysis of the electron localization function (ELF). A long C-C attractive interaction (3.077 Å) along the c axis of the cerussite structure is evidenced by the presence of bond critical points between the C atoms of the CO(3)(2-) molecular groups. It is proposed that the Pb-O interactions, which are mostly ionic in nature, disturb the structure of the CO(3)(2-) molecular groups and promote their interaction along the c axis. The importance of this long-range interaction in the high-pressure crystal chemistry of carbonate minerals and in the explanation of some crystal growth features observed for orthorhombic carbonates is also discussed in this work.

High pressure crystal chemistry

The application of high pressure techniques that stimulated the development of inorganic crystal chemistry, provided the discovery of new types of polymorphic transformations, showed the insufficiency of the ionic model to describe the crystal structures of even binary compounds, poses some unexpected theoretical questions.

Useful applications of the electron localization function in high-pressure crystal chemistry

The main features of a new computational code aimed at the topological analysis of the electron localization function (ELF) in crystals are hereby presented. Besides the complete localization of all critical points, the code is able to determine the limiting surfaces that define the chemical regions associated with the so-found maxima (or attractors) of the ELF. Hence, integrations of density operators within these basins provide charges and volumes to cores, bonds and lone pairs. Two illustrative applications have been selected. Firstly, we examine the Z dependence of basin compressibilities in the elements of the first two rows of the periodic table, and secondly, we focus our attention on the chemical changes across the pathway of the zinc blende–rocksalt phase transition in BeO.

High-pressure phase relations and crystal chemistry of calcium ferrite-type solid solutions in the system MgAl2O4-Mg2SiO4

To map the stability field of calcium ferrite-type MgAl2O4-Mg2SiO4 solid solutions, high-pressure phase relations in the system MgAl2O4-Mg2SiO4 were studied in the compositional range of 0 to 50 mol% Mg2SiO4. The calcium ferrite solid solutions are stable above 23 GPa at 1600 °C, and the maximum solubility of Mg2SiO4 component in MgAl2O4 calcium ferrite is 34 mol%. Lattice parameters and unit-cell volume of calcium ferrite-type MgAl2O4 (space group Pbnm) determined by Rietveld analysis are a = 9.9498(6) Å, b = 8.6468(6) Å, c = 2.7901(2) Å, and V = 240.02(2) Å3. Lattice parameters for the MgAl2O4-Mg2SiO4 solid solutions with the compositions of 14, 24, and 34 mol% Mg2SiO4 indicated the following compositional dependency of lattice parameters: a (Å) = 9.9498 + 0.1947·XMg₂SiO₄, b (Å) = 8.6468 . 0.1097·XMg₂SiO₄, and c (Å) = 2.7901 + 0.0086·XMg₂SiO₄, where XMg2SiO4 is the mole fraction of Mg₂SiO₄ component. A linear extrapolation of the composition-molar volume relationship gave an estimated volume of 36.49(2) cm3/mol for the hypothetical calcium ferrite-type Mg2SiO4. This value is larger than that of the isochemical mixture of MgSiO3 perovskite and MgO, 35.72(1) cm3/mol. This implies that the mixture of MgSiO3 perovskite and MgO is more stable than the hypothetical calcium ferrite-type Mg2SiO4 under the lower mantle conditions.

High-pressure crystal chemistry of binary intermetallic compounds

Abstract Effects of high pressure on intermetallic compounds are reviewed with regards to structural stability and phase transitions. Changes of bonding properties and electronic structure are examplified by means of the elemental metals caesium and titanium, the latter forming an internal intermetallic compound at high pressures. After a short systematic overview regarding pressure effects, structural transformations in selected classes of intermetallic compounds like Zintl phases and AlB2-type arrangements precedes sections concerning high-pressure synthesis of Laves phases and intermetallic clathrates.

High pressure crystal chemistry of hydrous ringwoodite and water in the Earth?s interior

The crystal chemistry of Fo90 hydrous ringwoodite (Mg1.7Fe0.22H0.15SiO4) containing 0.93% H2O by weight has been studied at pressures up to 11.2 GPa by single-crystal X-ray diffraction in the diamond anvil cell. The unit cell edge and volume have been refined at 20 different pressures in this pressure range. The refined bulk modulus for the unit cell is 169.0±3.4 GPa with a K′ of 7.9±0.9. H is accommodated in the structure principally by octahedral cation vacancy. The oxygen position parameter has been refined from X-ray intensity data at 10 pressures over this range. With a K′ fixed at 4.0, the bulk modulus of the Si tetrahedron is 245±31 GPa and that of the octahedral site is 150±7 GPa. Consistent with a previous study, we observe a systematic decrease of bulk modulus with H-content. From these data, it appears that hydration of ringwoodite has a larger effect on seismic velocity than temperature within the possible ranges of these parameters under upper mantle conditions. This means that in tomographic images of the Transition Zone in regions distant from subduction zones, blue is more likely to mean ‘dry’ than it is to mean ‘cold’. Observed seismic velocities in the Transition Zone are consistent with significant hydration of the ringwoodite (γ-(Mg, Fe)2SiO4) structure.

High pressure crystal chemistry of hydrous ringwoodite and water in the Earth’s interior

The crystal chemistry of Fo 90 hydrous ringwoodite (Mg 1.7Fe 0.22H 0.15SiO 4) containing 0.93% H 2O by weight has been studied at pressures up to 11.2 GPa by single-crystal X-ray diffraction in the diamond anvil cell. The unit cell edge and volume have been refined at 20 different pressures in this pressure range. The refined bulk modulus for the unit cell is 169.0±3.4 GPa with a K′ of 7.9±0.9. H is accommodated in the structure principally by octahedral cation vacancy. The oxygen position parameter has been refined from X-ray intensity data at 10 pressures over this range. With a K′ fixed at 4.0, the bulk modulus of the Si tetrahedron is 245±31 GPa and that of the octahedral site is 150±7 GPa. Consistent with a previous study, we observe a systematic decrease of bulk modulus with H-content. From these data, it appears that hydration of ringwoodite has a larger effect on seismic velocity than temperature within the possible ranges of these parameters under upper mantle conditions. This means that in tomographic images of the Transition Zone in regions distant from subduction zones, blue is more likely to mean ‘dry’ than it is to mean ‘cold’. Observed seismic velocities in the Transition Zone are consistent with significant hydration of the ringwoodite (γ-(Mg, Fe) 2SiO 4) structure.

Pressure-Induced Volume Expansion of Zeolites in the Natrolite Family

Powder diffraction patterns of the zeolites natrolite (Na(16)Al(16)Si(24)O(80).16H(2)O), mesolite (Na(5.33)Ca(5.33)Al(16)Si(24)O(80).21.33H(2)O), scolecite (Ca(8)Al(16)Si(24)O(80).24H(2)O), and a gallosilicate analogue of natrolite (K(16)Ga(16)Si(24)O(80).12H(2)O), all crystallizing with a natrolite framework topology, were measured as a function of pressure up to 5.0 GPa with use of a diamond-anvil cell and a 200 microm focused monochromatic synchrotron X-ray beam. Under the hydrostatic conditions mediated by an alcohol and water mixture, all these materials showed an abrupt volume expansion (ca. 2.5% in natrolite) between 0.8 and 1.5 GPa without altering the framework topology. Rietveld refinements using the data collected on natrolite show that the anomalous swelling is due to the selective sorption of water from the pressure-transmission fluid expanding the channels along the a- and b-unit cell axes. This gives rise to a "superhydrated" phase of natrolite with an approximate formula of Na(16)Al(16)Si(24)O(80).32H(2)O, which contains hydrogen-bonded helical water nanotubes along the channels. In mesolite, which at ambient pressure is composed of ordered layers of sodium- and calcium-containing channels in a 1:2 ratio along the b-axis, this anomalous swelling is accompanied by a loss of the superlattice reflections (b(mesolite) = 3b(natrolite)). This suggests a pressure-induced order-disorder transition involving the motions of sodium and calcium cations either through cross-channel diffusion or within the respective channels. The powder diffraction data of scolecite, a monoclinic analogue of natrolite where all sodium cations are substituted by calcium and water molecules, reveal a reversible pressure-induced partial amorphization under hydrostatic conditions. Unlike the 2-dimensional swelling observed in natrolite and mesolite, the volume expansion of the potassium gallosilicate natrolite is 3-dimensional and includes the lengthening of the channel axis. In addition, the expanded phase, stable at high pressure, is retained at ambient conditions after pressure is released. The unprecedented and intriguing high-pressure crystal chemistry of zeolites with the natrolite framework topology is discussed here relating the different types of volume expansion to superhydration.

High Pressure Crystal Chemistry of Transition Metal Diantimonides

High-pressure crystal chemistry of transition metal diantimonides is discussed. Two types of pressure-induced phase transitions, marcasite-type to CuAl2-type and marcasite-type to pararammelsbergite-type, occur in this family. The former is found in CrSb2 and the transition is accompanied by a change in bonding character from the mixed ionic and covalent to metallic. The latter is found in NiSb2 and can be explained by effective packing of NiSb6 octahedra. The local environment of nickel atom remains unchanged during the transition. The phase transition sequences in transition metal diantimonides, together with other dipnictides and dichalcogenides, are schematically summarized.

High-pressure crystal chemistry of chromous orthosilicate, Cr 2 SiO 4 . A single-crystal X-ray diffraction and electronic absorption spectroscopy study

The high-pressure behaviour of chromous orthosilicate, Cr2SiO4, has been studied by means of single-crystal X-ray diffraction and electronic absorption spectroscopy. X-ray diffraction data show that the structure remains orthorhombic to the highest pressure reached of 9.22 GPa. The compressibility of the unit-cell is strongly anisotropic with the c axis approximately six times more compressible than the a and b axes. A third-order Birch-Murnaghan equation of state fitted to the volume-pressure data yields V0 = 610.10(3) A3, K = 94.7(4) GPa, K′ = 8.32(14). Cr2SiO4 is therefore more compressible than the isostructural Cd analogue, even though its molar volume is smaller. This unusual behaviour can be attributed to the fact that the Cr atom is too small for the six-coordinated site that it occupies, and the site is therefore strongly distorted. Structure refinements indicate that under high pressures the Cr atom remains strongly displaced from the central position of the octahedron. Polarized and unpolarized electronic absorption spectra include a strong absorption band occuring at 18.300 cm−1 for E//c (which is parallel to the shortest Cr-Cr vector in the structure) which has an unusually large half width (5000 cm−1), indicative of electronic interaction between metal centres. Deconvolution of unpolarized high-pressure spectra show that the relative integrated intensity of this component increases linearly from 40% at 1 bar to 60% at 11.2 GPa. Both the structural changes and the absorption spectra at high pressures suggest that pairs of adjacent Cr atoms in chromous orthosilicate form chromium dimers with a weak metal-metal bond, which is consistent with the diamagnetic response found at ambient pressure.

Comparative high-pressure crystal chemistry of karrooite, MgTi2O5, with different ordering states

Two karrooite crystals, one with a disorder parameter (X = Ti content in the M1 site) of 0.070(5) and the other with X = 0.485(5), were mounted together in one diamond-anvil cell and studied by single-crystal X-ray diffraction at several pressures up to 7.51 GPa. The most noticeable effect of increasing cation disorder on the high-pressure behavior of the structure is to increase the compressibilities of the mean <M2-O> bond length from 0.00148(2) GPa -1 in the ordered sample to 0.00163(7) GPa -1 in the disordered one and decrease those of the mean <M1-O> bond length from 0.00243(5) to 0.00193(12) GPa -1 . These changes are responsible for the compressibility difference between the two phases observed by Hazen and Yang (1997). Both compressibilities of the mean <M-O> bond lengths and the octahedral volumes in two phases decrease linearly with increasing the Ti contents in the octahedral sites. All octahedra in two samples become less distorted as pressure increases, but those in the more disordered structure exhibit larger decreases in terms of the octahedral angle variance than the corresponding ones in the more ordered structure. The influence of pressure on the interatomic angles is small compared to the interatomic distances, suggesting that compression of the karrooite structure is controlled primarily by the bond-length shortening, rather than by bond-angle bending. The strong compressional anisotropy of the structure is a consequence of the differential compressibilities of the weaker Mg 2+ -O and stronger Ti 4+ -O bonds and the complex edge-sharing linkage involving the M1 and M2 octahedra.

High-pressure crystal chemistry of LiScSiO4; an olivine with nearly isotropic compression

Single-crystal X-ray diffraction data have been obtained at several pressures to 5.6 GPa for synthetic LiScSi04 olivine. The bulk modulus is 118 :t I GPa, assuming K' = 4. This value is smaller than that of forsterite because compressibility of Li-O bonds in the M1 octahedral site is approximately twice that of the MP+-O bonds in other isomorphs. Compressibilities of a, b, and c orthorhombic axes are 2.70, 2.80, and 2.61 (all x 10-3 GPa-1), respectively. This nearly isotropic compression (axial compression ratios = 1.00: 1.04:0.97) contrasts with that offorsterite (1.00: 1.99:1.55), fayalite (1.00:2.83: 1.22), monticellite (1.00: 1.85:1.10), and chrysoberyl (1.00: 1.30:1.17). These differences arise from the distinctive distribution of cations of different valences and consequent differences in M 1-0 and M2-0 bond compressibilities. The Li M 1 octahedron displays a significant decrease in polyhedral distortions with pressure, a behavior not observed in other olivines.