The ambient-temperature compressibility and room-pressure thermal expansion of two Mg3(PO4)2 polymorphs (farringtonite = Mg3(PO4)2-I, with 5- and 6-fold coordinated Mg, and chopinite = “Mg-sarcopside” = [6]Mg3(PO4)2-II), three Mg2PO4OH polymorphs (althausite, hydroxylwagnerite and ε-Mg2PO4OH, all with [5]Mg and [6]Mg) and phosphoellenbergerite ([6]Mg) were measured on synthetic powders using a synchrotron-based multi-anvil apparatus to 5.5 GPa and a laboratory high-temperature diffractometer, with whole-pattern fitting procedures. Bulk moduli range from 64.5 GPa for althausite to 88.4 GPa for hydroxylwagnerite, the high-pressure Mg2PO4OH polymorph. Chopinite, based on an olivine structure with ordered octahedral vacancies (K0 = 81.6 GPa), and phosphoellenbergerite, composed of chains of face-sharing octahedra (K0 = 86.4 GPa), are distinctly more compressible than their homeotypical silicate (127 and 133 GPa, respectively). The compressibility anisotropy is the highest for chopinite and the lowest for phosphoellenbergerite. First-order parameters of quadratic thermal expansions range from v1 = 2.19×10-5 K−1 for ε-Mg2PO4OH to v1 = 3.58×10-5 K−1 for althausite. Phosphates have higher thermal-expansion coefficients than the homeotypical silicates. Thermal anisotropy is the highest for farringtonite and the lowest for hydroxylwagnerite and chopinite. These results set the stage for a thermodynamic handling of phase-equilibrium data obtained up to 3 GPa and 1000 °C in the MgO–P2O5–H2O and MgO–Al2O3–P2O5–H2O systems.

Multiferroic ceramics with switchable magnetization as well as high polarization at room temperature have remarkable technological impact. Herein, we report that a small concentration of Fe doping in the B-site of sodium bismuth titanate (NBT) lead to room temperature multiferroic nature with fascinating properties. The key factor responsible for the embellished multiferroic behavior at room temperature was electric field induced non-180 degrees domain alignment bridged with dynamic exchange interaction of trapped electrons in ordered polarons. The optimum doping of 0.02 mole fractions Fe in NBT favored ferromagnetic loop with highest remanence of 198 memu/g and coercive field 133 Oe along with improved ferroelectric polarization of 31.8 mC/cm(2) and a strong self-biased direct magnetoelectric coupling coefficient of 7.38 mV/cmOe. Strong coupling at low ac field, high reliability, easy control by an electric signal and fast switching behavior add importance to this lead-free Fe-doped sodium bismuth titanate ceramic as potential material, applicable in biocompatible magnetic sensors. (c) 2020 Elsevier B.V. All rights reserved.

The conclusion of Zaffiro et al. (2019; Constraints on the Equations of State of stiff anisotropic minerals: rutile, and the implications for rutile elastic barometry. Mineralogical Magazine, 83, 339-347) that the Mie-Gruneisen-Debye (MGD) Equation of State (EoS) cannot fit the available data for rutile is shown to be incorrect, even though rutile exhibits significant anisotropic thermal pressure which invalidates the quasi-harmonic approximation used as the basis for the MGD EoS. The refined parameters for the MGD EoS of rutile are: K-TR0=205.05(25) GPa, K-TR0' = 7.2(5), theta(D) = 399(20) K, gamma(0)=1.40(2) and q = 1.5(7). This EoS predicts volumes, bulk moduli and volume thermal expansion coefficients for rutile at metamorphic conditions that are statistically indistinguishable from those predicted by the 'isothermal' type of EoS reported previously.

Based on the high abundance of fine‐grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite–cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe‐rich olivine during a heating event without changing the textural appearance. A peak temperature of 400–600 °C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot‐like inclusions (UCLIs) within fine‐grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine‐grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice‐rich first‐generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.

The search for multiferroic order in a single phase of bismuth pyrochlore has been unsuccessful so far. In this direction, our study unveiled the capability of a biphase of bismuth pyrochlore and spinel in hosting a multiferroic order at room temperature. A complex oxide biphase of cubic pyrochlore and cubic spinel crystals acquired in the Bi2O3-Nb2O5-2MnCO3-Fe2O3 system revealed the crystals of a spinel phase (Fe1.59(3)Mn1.39(3)O4.26(7)) intergrown in the dense pyrochlore (Bi1.35(1)Fe0.64(1)Nb1.26(1)Mn0.75(1)O6.39(5)) matrix. The average composition of the components of the investigated biphase was determined using an electron probe microanalyzer (EPMA). The structural features indicated the presence of large ionic displacements within the cubic pyrochlore phase as seen from the appearance of 442 reflection in the X-ray diffraction pattern and infrared active mode at ∼64 cm−1 in the Raman spectrum recorded at room temperature. The pyrochlore single-phase composition (Bi1.35(1)Fe0.64(1)Nb1.26(1)Mn0.75(1)O6.39(5)), as suggested from a thorough EPMA microstructural analysis, exhibited broad dielectric relaxation and an overall paramagnetic behavior. The observation of disordered superparamagnetism as well as dielectric relaxation in the biphase conformed to that of a relaxorlike multiferroic behavior at room temperature. Moreover, self-biased magnetoelectric voltage coefficients of 0.60 mV/cm Oe at 100 Hz and 5.54 mV/cm Oe at 1 kHz were detected between magnetization and electric polarization at room temperature. Therefore, the composite of such a pyrochlore and spinel with an inherent property of strong spin–orbit and spin–lattice coupling will be interesting from theoretical and experimental point of view in the arena of magnetoelectrics.

To complete the data basis for comparing the thermal behaviour of end-member olivines containing cations of the transition element series Mn (3d(5)), Fe (3d(6)), Co (3d(7)), Ni (3d(8) subshell) the thermal expansivity of Co and Ni olivines has been studied by X-ray powder diffraction at ambient pressure and temperatures between 25 degrees C and 1000 degrees C. The anisotropy of the thermal expansion was analysed using the Kumar isothermal equation-of-state (EoS) coupled with the thermal Mie-Griineisen EoS. For Co olivine, in order to stabilize the refinement of the EoS coefficients, our thermal expansion data were combined in a simultaneous fit with published P(a, b, c, V) and axial and bulk K-T (T) data. This reduced correlations between parameters considerably. Analogous pressure and moduli data for Ni olivine are lacking so that only unit-cell data could be fitted. The volume related EoS of Co olivine are K-0(T)=143.7(3) GPa, K-0(T') = 5.0(2), gamma(MG)(0) = 1.23(1), V-0 = 295.69(5) angstrom(3) with the acoustic Debye temperature fixed at 551 K. Axial expansivities a are controlled by compressibilities beta(T)-and thermal pressures (partial derivative P/partial derivative T)(V) according to alpha = beta(T)(partial derivative P/partial derivative T)(V). For olivines, the structural features suggest a sequence of compressibilities with beta(T,b) > beta(T),(c) > beta(T,a) (SG Pbnm). Usually, a similar ranking is also found for the axial expansivities. In the case of olivines, however, only Mn olivine meets the expectation, contrary to Fe olivine and to a lesser extent to Co and Ni olivine. The reason for the unusual behaviour is found in the specific anisotropies of the axial thermal pressures. Extrapolation of thermal expansivities and of linear and bulk moduli is justified up to 2200 K, judged from the fulfillment of the relations 1/K-V(T) = (1/3K(a)(T) + 1/3K(b)(T) +1/3K(c)(T)) and alpha(V)(T) = alpha(a)(T) alpha(b)(T) + alpha(c)(T)

Iron (Fe) incorporated intergrown pyrochlore-spinel phase of nominal compositions BiNbFe0.1Mn1.9O7-delta(BNFMO), BiTaFe0.1Mn1.9O7-delta (BTFMO) and BiSbFe0.1Mn1.9O7-delta (BSFMO) were synthesized by solid state reaction. The replacement of 5% iron (Fe) for JahneTeller active manganese (Mn) in the composites tuned the magnetic ordering to higher temperature (75 K-89 K) without having much effect on the structure of the constituent phases of the composite. Fe incorporated hausmannite crystals were uniformly scattered and appeared to be occluded within the pyrochlore grains which instilled interest in the study of this system. Ac susceptibility and temperature dependent dielectric studies of BNFMO composite indicated spin disorder as well as broad dielectric relaxation, respectively. Occurrence of magnetic ordering observed in the composite was mostly due to hausmannite secondary phase. The unavoidable crystallization of secondary phase by slow cooling prompted us to further explore and get an insight into this naturally favoring composite. The uniform distribution of hausmannite phase, structural similarity of pyrochlore and spinel lattice and their intergrowth seems to be interesting for hosting multiferroic order. (C) 2018 Elsevier B.V. All rights reserved.

Low temperature spin glass like behavior and high temperature dielectric relaxation have been observed in BNMO pyrochlore–spinel composites.

In order to assess the stability of the primary triphylite + sarcopside assemblage, we performed hydrothermal experiments between 400 and 700 C-omicron (Ni/NiO oxygen fugacity buffer, P = 1 kbar), starting from the Li(Fe2.5-x2+Mnx2+)(PO4)(2) (x = 0.0, 0.5, 1.0) compositions, which represent the ideal compositions of triphylite + sarcopside assemblages in which both minerals occur in a 1: 1 molar ratio. The triphylite + sarcopside assemblage is observed in all experiments, associated with other phosphates like (Fe2+, Mn2+)(2)P2O7, (Fe2+, Mn2+) Fe-2(3+)(PO4)(2)(OH)(2) center dot nH(2)O, or Fe-4(3+)(Fe2+, Mn2+) (3)(PO4)(6). Electron-microprobe and SIMS analyses show a progressive decrease of the Li contents in the triphylites, balanced by an increase of their Fe2+-contents, when the temperature increases. These compositional changes are due to the increase of the triphylite-sarcopside miscibility along the Li-2(Fe2+, Mn2+)(2)(PO4)(2)-Fe2+(Fe2+, Mn2+)(2)(PO4)(2) solid solution; the experimental phase diagrams can consequently be used as a geothermometer to calculate the exsolution temperatures of the assemblages. A linear fit of the experimental data leads to the general equation: T(C-omicron) = (-142 * XFe) - (773 * Li pfu) + 1131, where XFe = Fe/(Fe + Mn). The uncertainty is around +/- 15 C-omicron, and the influence of pressure is assumed to be negligible. By using this equation, exsolution temperatures were calculated for nine triphylite-sarcopside assemblages from pegmatites; these temperatures do not represent the crystallization temperatures of the phosphate nodules, but correspond to the closing temperature of the triphylite-sarcopside element exchange. Nevertheless, these temperatures, between 276 and 397 C-omicron, are in fairly good agreement with those generally accepted for the crystallization of primary phosphate assemblages in granitic pegmatites.

The crystal structure of CoMg olivine has been investigated by in situ neutron and synchrotron X-ray powder diffraction at temperatures between 23 degrees C and 1050 degrees C. The olivine sample was prepared at 1450 degrees C by solid-state reaction. During quench, the structure acquired a partially anti-ordered Co, Mg site occupancy, X-Co(M1)>X-Co(M2), which upon ensuing heating persisted up to 550 degrees C due to slow exchange kinetics. Above 600 degrees C, internal equilibrium was readily obtained. The temperature variation of the Co, Mg site occupancies was modelled by RT ln(K-D) = -12080 (+/- 620) - 1.60(+/- 0: 58) T [J mol(-1)]. The pronounced negative exchange enthalpy strongly favours the anti-ordered state, as does the positive exchange entropy so that CoMg olivine will remain in this state up to the melting point.The anisotropy of thermal expansion was analysed using an isothermal equation-of-state (EoS) (Kumar, 1995) coupled with the thermal Mie-Gruneisen EoS. This coupling allowed for relating the anisotropic expansivity to an anisotropic thermal pressure. Both properties are linked to the temperature-dependent rotations of the M1 and M2 octahedra in the [ 001] plane. The rotations increase from Mg via CoMg to Fe olivine. The Kumar and Birch-Murnaghan EoS's gave virtually indistinguishable results upon modelling thermal expansion.The increase of the mean bond distances < M1-O > and < M2-O > with temperature changes at similar to 550 degrees C when the redistribution of Co and Mg begins. In terms of a distortion parameter defined as a normalized standard deviation, the bond length distortion of the M2 octahedron is larger than that of M1. Conversely, M1 is more distorted than M2, if the distortion is defined by the variation of the octahedral faces as well as by the variation of the O-M-O angles subtended at the M sites. The former distortion relates to the exchange entropy.

We present a new strategy on how to synthesize trace-element bearing (REE, Sr) chlorapatites Ca5(PO4)3Cl using the flux growth method. Synthetic apatites were up to several mm long, light blue in colour. The apatites were characterized using XRD, electron microprobe and laser ablation ICP-MS (LA-ICPMS) techniques and contained several hundred μg/g La, Ce, Pr, Sm, Gd and Lu and about 1700 μg/g Sr. The analyses indicate that apatites were homogenous (within the uncertainties) for major and trace elements.

The topotactic oxidation and delithiation reaction from triphylite, Li(Fe,Mn)PO 4 , leading to ferrisicklerite, Li <1 (Fe 3+ ,Mn 2+ )PO 4 , was investigated under hydrothermal conditions. A cuboid cut from a triphylite single-crystal (Palermo Mine, New Hampshire, USA) with the composition Li 0.93(3) (Fe 2+ 0.733(6) ,Fe 3+ 0.015(1) ,Mn 2+ 0.210(4) ,Mg 0.063(2) ) 1.021(8) P 1.00(2) O 4 in addition with ground bulk material were treated with KMnO 4 and 30 % H 2 O 2 (aq) as oxidizing agent in a 0.1 N hydrochloric acid solution in the temperature range between 60 and 200 °C. At 120 °C a rim of 0.1 mm thickness of ferrisicklerite had formed around the core of unreacted triphylite. The sharp reaction boundary was clearly visible, due to the reddish brown absorption colors of ferrisicklerite, compared to colorless triphylite. Using single-crystal X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), electron probe micro-analysis (EPMA) and 57 Fe-Mössbauer spectroscopy the product ferrisicklerite was characterized and its composition determined as Li 0.30(7) (Fe 2+ 0.049(1) Fe 3+ 0.65(2) Mn 2+ 0.218(5) Mg 0.062(2) ) 0.98(1) P 1.01(3) O 4 , with unit cell parameters a = 4.795(1), b = 9.992(4), and c = 5.886(2) Å. EPMA investigations across the reaction boundary showed no changes in the concentrations of Fe, Mn, Mg, and P. In contrast, SIMS measurements clearly proved the delithiated state of the ferrisicklerite product. Polarization microscopy revealed that the orientation of the ferrisicklerite rim was the same as that of the original triphylite single-crystal, confirming the strictly topotactic character of the reaction.

In order to assess the stability of the primary alluaudite + triphylite assemblage, we performed hydrothermal experiments between 400 and 800°C, starting from the LiNa2Mn x Fe 3−x 2+ Fe3+(PO4)4 compositions (x = 1.054, 1.502, 1.745) that represent the ideal compositions of the alluaudite + triphylite assemblages from the Kibingo (Rwanda), Hagendorf-Süd (Germany), and Buranga (Rwanda) pegmatites, respectively. The pressure was maintained at 1 kbar, and the oxygen fugacity was controlled by the Ni–NiO buffer. The results of these experiments show that the alluaudite + triphylite assemblage crystallizes at 400 and 500°C, while the association alluaudite + triphylite + marićite appears at 600 and 700°C. The limit between these two domains, at ca. 550°C, corresponds to the maximum temperature that can be reached by the alluaudite + triphylite assemblages in granitic pegmatites, because marićite has never been observed in such geological environments. At 800°C, the formation of the X-phase + triphylite assemblage indicates a strong reduction of the bulk composition, according to the reaction 0.5LiM2+PO4 (triphylite) + 3Na2M2 2+Fe3+(PO4)3 (alluaudite) + 1.5H2O = 4.5NaM2+PO4 (marićite) + Li0.5Na1.5M5 2+(PO4)4 (X-phase) + H3PO4 + 0.75O2 (M2+ = Fe2+, Mn). Secondary ion mass spectrometry (SIMS) was used at our knowledge for the first time to measure Li in all the Li-bearing phosphates. A specific methodological procedure was developed with the ion microprobe to get accurate Li2O data over a wide concentration range spanning from few ppm Li up to ~11 wt%. Li2O. Our SIMS analyses of the synthesized phosphates indicate that the Li contents of alluaudites, marićites, and X-phase increase progressively with temperature, while the Li content of triphylite-type phosphates decreases due to the Li → Na substitution. The Na-exchange equilibrium between triphylite-type phosphates and alluaudite is correlated with the temperature according to the equation: ln(x Na Tri /x Na All ) = −7.0(7) 103/T + 5.4(9). This equation can be used to estimate the crystallization temperature of triphylite–alluaudite assemblages independently of the oxygen fugacity.

Oxides with the nominal chemical compositions Li5La3Sb2O12 and Li6SrLa2Sb2O12 were prepared by solid-state reaction. The structures were refined by the Rietveld method using powder X-ray diffraction data. The synthesis of Li5La3Sb2O12 resulted in the well known garnet-related structure plus 5 wt.% of La2LiSbO6 in the bulk. In contrast to that, Li6SrLa2Sb2O12 could be synthesised in single garnet-related type phase. Lithium ion conductivities of Li5La3Sb2O12 and Li6SrLa2Sb2O12 were studied by the ac impedance method. The grain-boundary contribution to the total (bulk + grain-boundary) resistance is very small and about 5 and 3% for Li5La3Sb2O12 and Li6SrLa2Sb2O12, respectively, at 24 °C and decreases further with increase in temperature. Among the investigated compounds, Li5La3Sb2O12 exhibits the highest total (bulk + grain-boundary) and bulk ionic conductivity of 7.8 × 10−6 and 8.2 × 10−6 S cm−1, respectively, at 24 °C. The structural data indicate that the coupled substitution Li + Sr ⇒ La leads to a closure of the bottle neck like O–O distances of the shared edges of neighbouring Li octahedra and therefore reduces the mobility of Li ions in Li6SrLa2Sb2O12. Scanning electron microscope (SEM) images of the Li6SrLa2Sb2O12 compound revealed well crystallised large homogeneous grains (∼4.8 μm) and the grains were in good contact with the neighbouring grain, which leads to a smaller grain-boundary contribution to the total resistance.

Leucite and analcime have open framework aluminosilicate structures, where ion exchange by cation substitution has been previously used to explain the replacement of one phase by another. Using O-18-enriched NaCl solutions in hydrothermal reactions and run-product analyses using scanning electron microscopy, infrared and Raman spectroscopy, and time-of-flight secondary ion mass spectrometry, we show that the replacement of leucite by analcime is not a solid-state reaction involving cation exchange by volume diffusion. Textural features such as nano-pores and clusters, as well as the detection of high amounts of O-18 in the framework of analcime, suggest that the reaction proceeds by dissolution of leucite and reprecipitation of analcime, where structural O atoms of the leucite framework are exchanged and a new analcime structure forms at a moving interface through the leucite parent crystal. The characteristic high porosity (on a nano-scale) in the analcime product phase results from some of the parent phase being lost to the solution to give a volume deficit reaction. However, external dimensions are maintained during the process to result in the pseudomorphic replacement of an open framework aluminosilicate structure by a coupled dissolution-reprecipitation mechanism.

We report the synthesis, structure and transport properties of the new chemical compositions Li5La3Bi2O12 and Li6SrLa2Bi2O12. Qualitative phase analysis by X-ray powder diffraction patterns in combination with the Rietveld method revealed garnet type compounds as major phases. Whereas Li5La3Bi2O12 was found to be a single-phase material, BiLa2O4.5 could be identified as an impurity phase in the case of Li6SrLa2Bi2O12. Lithium ion conductivities of Li5La3Bi2O12 and Li6SrLa2Bi2O12 were studied by ac impedance method. The grain-boundary contribution to the total (bulk+grain-boundary) resistance is appreciable and amounts to about 54% and 61% for Li5La3Bi2O12 and Li6SrLa2Bi2O12, respectively, at 22°C. Li6SrLa2Bi2O12 exhibits the highest total (bulk+grain-boundary) and bulk ionic conductivity of 2.0×10−5 and 5.2×10−5S/cm, respectively, at 22°C. The bismuth containing lithium garnet exhibits a maximum cubic lattice constant and the best lithium ion conductivity with low activation energy in the Li5La3M2O12 (M=Ta, Nb, Sb and Bi) series.

The phase MgAlPO4O is a thermal decomposition product of the metamorphic phosphate mineral lazulite, MgAl2(PO4)(2)(OH)(2); its polymorphism and thermochemistry were investigated. The room-temperature beta ''-polymorph of MgAlPO4O was found to undergo an isosymmetric and reversible phase transition towards a non-quenchable alpha'-polymorph at 758 K (485 degrees C). The two structures are found to be closely related to each other. They are characterised by the presence of sheets of five-fold coordinated Mg and layers containing zweier single chains of Al-tetrahedra as well as additional PO4 groups providing a connection between the chains. Due to the specific linkage of the chains and the phosphate groups, a single tetrahedral layer consists of both twofold and fourfold connected tetrahedra in the ratio Q(4)Q(2) = 1:1. The beta ''-alpha' transition is accompanied by a transformation enthalpy of Delta H beta ''-alpha' = 0.65 kJ/mol (DSC measurement), a volume reduction of -2.3 % and it is characterised by switching of bonds between Mg2+ and the coordinating 01 ions. The corresponding negative Clapeyron slope of the transition implies that the beta ''-polymorph is stable in a restricted low-P (< 0.5 GPa) and low-T (< 758 K) field as confirmed by in situ X-ray diffraction experiments (MAX80, Hasylab). A third-law entropy value (S-298(0),) of 110.7(1) J/mol.K was obtained for beta ''-MgAlPO4O by heat-pulse calorimetry using the Physical Properties Measurement System (PPMS) produced by Quantum Design (R). The reaction 3 MgAlPO4O double left right arrow farringtonite + berlinite + corundum was bracketed up to 1373 K and 1 GPa in an internally heated pressure vessel. The combination of the experimental brackets with the PPMS entropy value allows us to derive a standard enthalpy of formation (Delta H-f,298(0)) of -2394(5) kJ/mol for beta ''-MgAlPO4O.