Stabilization Of The CN₃⁵− Anion In Recoverable High-pressure Ln₃O₂(CN₃) (Ln=La, Eu, Gd, Tb, Ho, Yb) Oxoguanidinates

A series of isostructural Ln(3)O(2)(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) oxoguanidinates was synthesized under high-pressure (25-54 GPa) high-temperature (2000-3000 K) conditions in laser-heated diamond anvil cells. The crystal structure of this novel class of compounds was determined via synchrotron single-crystal X-ray diffraction (SCXRD) as well as corroborated by X-ray absorption near edge structure (XANES) measurements and density functional theory (DFT) calculations. The Ln(3)O(2)(CN3) solids are composed of the hitherto unknown CN35- guanidinate anion-deprotonated guanidine. Changes in unit cell volumes and compressibility of Ln(3)O(2)(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) compounds are found to be dictated by the lanthanide contraction phenomenon. Decompression experiments show that Ln(3)O(2)(CN3) compounds are recoverable to ambient conditions. The stabilization of the CN35- guanidinate anion at ambient conditions provides new opportunities in inorganic and organic synthetic chemistry.Funding Agencies|National Science Foundation; DOE Office of Science by Argonne National Laboratory; UKRI Future Leaders Fellowship; Deutsche Forschungsgemeinschaft (DFG) [DE-AC02-06CH11357, MR/V025724/1, 2009 00971]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University; Projekt DEAL; [DU 954-11/1]; [DU 393-9/2]; [DU 393-13/1]; [DU 945/15-1]; [EAR- 1634415]</p

Chemical reactivity of pozzolans from Sardinia for the production of hydraulic limes

The research is aimed at studying the chemical reactivity between lime and volcanic rocks belonging to different Sardinian outcrops, for a use as raw material in the production of hydraulic / pozzolanic limes. On the basis of preliminary geochemical and mineralogical-petrographic investigations, several volcanic rocks with a basic-intermediate to acid composition (substantially from andesitic, to dacitic, to rhyolitic) have been selected and used for to perform laboratory reactivity tests. These rocks differ in the variable content of glass (from 15% to about 95% in volume), due to the presence of secondary minerals, and to physical characteristics (density, porosity, water absorption, etc.). The physical properties are essentially linked to the different compositional incidence of the crystalline, crystal-clastic, lithic (present in some pyroclastic facies), type and quantity of glass phases, to their different methods of installation (conditioned by temperature, chemical composition, grade welding, etc.), and to the different degree of alteration. The results of the investigations on the pozzolan materials (by polarized light microscopy, XRD, SEM, EPMA-WDS, Chapelle test) show that following parameters affect the chemical reactivity of the volcanic products with lime: i) quantity and type of amorphous phases (glass), linked to the different emplacement of volcanic rocks (affected by temperature, chemical composition, welding grade, etc.), ii) compositional incidence of the crystalline phases, crystal-clasts, lithics (these latter present in some pyroclastic facies), iii) alteration grade of the rocks and presence of secondary minerals (e.g., zeolites, phyllosilicates, etc.)

High-pressure behavior and phase transition in colemanite, an inoborate

Colemanite, CaB3O4(OH)3 x H2O, is a common constituent of natural borate deposits and a relevant mineral commodity, for its applications in the B-extraction processes and in the production of lightweight cements and ceramics [1,2]. Its crystal structure is monoclinic (P21/a, a = 8.712 Å, b = 11.247 Å, c = 6.091 Å, β = 110.12°, V = 560.4 Å3), characterized by infinite chains of Bpolyhedra based on a fundamental ring-unit made by one triangular BO3 and two B(O,OH)4 tetrahedra. These chains are alternated with chains of Ca-polyhedra (coordination number, CN =8), giving rise to sheets parallel to (010). Adjacent sheets are mainly interconnected through an H-bonding system involving hydroxyl groups and H2O molecules. The links among structural polyhedra, both B and Ca, are all corner sharing in type [3]. Despite its relevance in industrial applications, the behavior of colemanite at high pressure has never been investigated. In this work, we have characterized the elastic behavior, the phase stability, the phase transition and the structural evolution with pressure of a natural colemanite single crystal based on an in-situ synchrotron X-ray diffraction study, performed at the P02.2 beamline of PETRA-III, Hamburg, Germany. Colemanite, in its ambient conditions polymorph, is found to be stable up to 13.95 GPa. A IIIorder Birch-Murnaghan (III-BM) EoS fit leads to a refined bulk modulus (at ambient conditions) (KV0) of 76(8) GPa [K = 4.4(10)]. Comparative structure analysis, based on the refinements of the structure model at different pressures, shows that the B-polyhedra act as quasi-rigid units and the bulk compression is mainly accommodated by the compression of Ca-polyhedra and by polyhedral tilting. Between 13.95 and 14.91 GPa, colemanite undergoes a reconstructive phase transition toward a monoclinic polymorph (P21/n, a = 11.726(11) Å, b = 10.206(1) Å, c = 23.45(3) Å, β = 95.07(9)°, V = 2796(4) Å3, at 14.91 GPa). The average coordination number of boron is found to increase: of the 18 independent B sites, 3 are triangularly coordinated and 15 are tetrahedra. Two independent infinite chains of B-polyhedra are alternated with two independent chains of Capolyhedra (CN = 8 or 9), by means of corner- and edge-sharing links. A II-BM EoS fit leads to a refined KV0 of 60(6) GPa for the high-P polymorph of colemanite. X-ray diffraction patterns collected during P-release show that the phase transition is completely reversible and colemanite fully recovers its starting structural features. [1] K. Okuno Radiat. Prot. Dosim. 2005, 115, 258-261. [2] A. Christogerou, T. Kavas, Y. Pontikes, S. Koyas, Y. Tabak, G.N. Angelopoulos Ceram. Int. 2009, 35, 447-452. [3] P.C. Burns, F.C. Hawthorne Can. Mineral. 1993, 31, 297-304

From Nature to materials science: (Cs,K)Al4Be5B11O28(Cs,K)Al_{4}Be_{5}B_{11}O_{28} (londonite) as a super-hard material

Londonite is a rare Cs-bearing mineral with ideal chemical formula (Cs,K)Al4Be4(B,Be)12O28 (with Cs > K). The building block units of the structure of londonite are represented by clusters of four edge-sharing Al-octahedra linked to B- and Be-tetrahedra. Gatta et al. (2011) investigated the phase stability and the elastic behavior of londonite up to 4.85(5) GPa (at room-T) and up to 1000°C (at room-P) by in situ X-ray powder diffraction data, but no structure refinements were possible. Whether no phase transition was observed within the pressure-range investigated, londonite proved to have an extremely high bulk modulus: KP0 = 280(12) GPa, similar to those of carbides (e.g., B4C with KP0 ~ 245-306 GPa; Lazzari et al., 1999; Fujii et al., 2010). Considering the thermo-elastic properties and the significantly high fraction of boron (B2O3 ~50 wt%), the synthetic counterparts of londonite could be considered a potential inorganic host for 10B in composite neutron-absorbing materials. Furthermore the high content of Cs makes londonite-type materials potential host for nuclear waste. However, to date, because of the absence of structural data at high pressure and to the modest P-range investigated by Gatta et al. (2011), a comprehensive description of the P-induced deformation mechanisms at the atomic scale is still missing. In this study, the isothermal compressional behaviour of londonite is studied by in situ single-crystal synchrotron X-ray diffraction experiment with a diamond anvil cell up to 25 GPa. The compressional behavior and the deformation mechanisms at the atomic scale are described. Londonite does not experience any phase transition or change of the compressional behavior within the P-range investigated.Fujii, T., Mori, Y., Hyodo, H., Kimura, K. (2010): X-ray diffraction study of B4C under high pressure. J. Phys. Conf. Ser., 215, 012011. Gatta, G.D., Vignola, P., Lee, Y. (2011): Stability of (Cs,K)Al4Be5B11O28 (londonite) at high pressure and high temperature: a potential neutron absorber material. Phys. Chem. Miner., 38, 429-434. Lazzari, R., Vast, N., Besson, J.M., Baroni, S., Dal Corso, A. (1999): Atomic structure and vibrational properties of icosahedral B4C boron carbide. Phys. Rev. Letters, 83, 3230-3233

Fig1Data_Hannaetal

Fig1Data_Hannaeta

Wardite (NaAl3(PO4)(2)(OH)(4)Greek ano teleia2H(2)O) at High Pressure: Compressional Behavior and Structure Evolution

International audienceThe high-pressure behavior of wardite, NaAl3(PO4)(2)(OH)(4)center dot 2H(2)O (a = 7.0673(2) angstrom, c = 19.193(9) angstrom, Sp. Gr. P4(1)2(1)2), 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: V-0 = 957.8(2) angstrom(3) and K-V0 = -V-0( partial differential P/ partial differential V)(P0),(T0) = 85.8(4) GPa (beta(V0) = 1/K-V0 = 0.01166(5) GPa(-1)). Axial bulk moduli were also calculated, with: K-0(a) = 98(3) GPa (beta(0(a)) = 0.0034(1) GPa(-1)) and K-0(c) = 64(1) GPa (beta(0(c)) = 0.0052(1) GPa(-1)). The anisotropic compressional scheme is: K-0(a):K-0(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

Wardite (NaAl3(PO4)2(OH)4·2H2O) at High Pressure: Compressional Behavior and Structure Evolution

The high-pressure behavior of wardite, NaAl3(PO4)2(OH)4&middot;2H2O (a = 7.0673(2) &Aring;, c = 19.193(9) &Aring;, 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&ndash;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) &Aring;3 and KV0 = &minus;V0(&part;P/&part;V)P0,T0 = 85.8(4) GPa (&beta;V0 = 1/KV0 = 0.01166(5) GPa&minus;1). Axial bulk moduli were also calculated, with: K0(a) = 98(3) GPa (&beta;0(a) = 0.0034(1) GPa&minus;1) and K0(c) = 64(1) GPa (&beta;0(c) = 0.0052(1) GPa&minus;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

Armstrongite at non-ambient conditions: An in-situ high-pressure single-crystal X-ray diffraction study

The high-pressure behavior of a natural armstrongite [(Ca0.96Ce0.01Yb0.01)Zr0.99Si6O14.97·2.02H2O, a∼14.03 Å b∼14.14 Å c∼7.85 Å β∼109.4° Sp. Gr. C2/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:H2O = 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 (KV0= -V (∂P/∂V)) of the high-pressure polymorph was found to be ∼50% higher than that obtained for the low-pressure one (i.e., KV0= 45 (1) GPa for the high-pressure polymorph, KV0= 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

Correction to: Allanite at high pressure: effect of REE on the elastic behaviour of epidote-group minerals

The compressional behaviour of a natural allanite from Lago della Vecchia (upper Cervo valley, Italy) metagranitoids[$^{A1}$(Ca$_{0.69}$Fe$^{2+}$$_{0.31}$)$_{Σ1.00}^{A2}$(Ca$_{0.46}$Ce$_{0.24}$La$_{0.12}$Sm$_{0.02}$Pr$_{0.05}$Nd$_{0.09}$Th$_{0.02}$)$_{Σ1.00}^{M1}$(Al$_{0.65}$Fe$^{3+}$$_{0.34}$Ti$_{0.02}$)$_{Σ1.01}^{M2}$(Al$_{0.99}$)$^{M3}$(Fe$^{3+}_{0.54}$Fe$^{2+}_{0.36}$Mg$_{0.06}$Ti$^{4+}_{0.02}$Al$_{0.01}$)$_{Σ0.99}$ $^{Si1,Si2,Si3}$(Si$_{2.80}$Al$_{0.20}$)$_{Σ3.00}O_{11}$(OH,O)] has been investigated up to 16 GPa (at 298 K) by means of in situsynchrotron single-crystal X-ray diffraction. Experiments have been conducted under hydrostatic conditions, using a diamondanvil cell and the mix methanol:ethanol:water = 16:3:1 (up to 10 GPa) and neon (up to 16 GPa) as pressure-transmittingmedia. No phase transition has been observed within the pressure-range investigated. Data collected in decompression provethat, at least up to 16 GPa (at 298 K), the deformation mechanisms are fully reversible. A third-order Birch–MurnaghanEquation of State (BM-EoS) was fitted to the P–V data (up to 10 GPa), giving: V$_0$ = 470.2(2) Å$^3$, K$_{P0,T0}$ = 131(4) GPa andK′= 1.9(8). The evolution of the lattice parameters with pressure shows a slight anisotropic compression pattern, with K$_{P0,T0}$(a):K$_{P0,T0}$(b):K$_{P0,T0}$(c) = 1.24:1.52:1. The monoclinic β-angle decreases monotonically with pressure, with: $β_{P}(°)$ = $β_{P0}$ – 0.0902(4)P (R$^2$ = 0.997, with P in GPa). The main deformation mechanisms at the atomic scale are described basedon a series of structure refinements at different pressures. A comparison between the compressional behavior of allanite,epidote and clinozoisite is carried out