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We report here the preparation and characterization of two families of RP 2D perovskites including linear monoammonium cations, namely (CnH2n+1NH3)2PbBr4 and (CnH2n+1NH3)2PbI4 with n = 4, 6, 8, 10, 12, 14 and 16.

Earthquakes are generated through the brittle failure of rocks at depth. While earthquakes are generally caused by far–field tectonic stresses, the atomic–scale mechanisms that actually trigger brittle failure in dry ductile crustal rocks are still uncertain. Quartz, a widespread mineral in the lower crust, undergoes an instantaneous polymorphic transformation from the α to β phase at pressure and temperature conditions compatible with the estimates of several lower–crustal paleo–earthquakes recorded as pseudotachylytes. The α–β quartz transition is displacive, reversible and, as α–quartz approaches the transition temperature at constant pressure, its volume increases non–linearly but without sudden jumps. In contrast, near the phase–transition temperature, the bulk modulus of quartz drops from ~30 GPa to almost zero and then abruptly rises to more than 70 GPa within a temperature range of only 10 K (Lakshtanov et al., 2007).Due to the confined space, near the α–β transition, a quartz inclusion in a garnet host is expected to develop strong differential strains and consequently will impose strong differential stresses on the surrounding host crystal. To check this hypothesis, we have applied in situ high–temperature Raman spectroscopy to quartz inclusions in garnet to monitor the development of structural deformation via the atomic dynamics at temperatures across the phase transition temperature Tc = 847 K for a free quartz crystal at atmospheric pressure. The temperature behaviour of the phonon wavenumbers ω of a quartz inclusion, in particular the hardening and disappearance of a minimum in ω(T) for the A modes near 208 and 464 cm-1 (involved in the α-β phase transition) as well as the persistence of Raman activity of the modes at ~128 cm-1 and ~355 cm-1 above Tc, reveals the accumulation of abnormally high strain in the confined quartz grains in the vicinity of the expected phase transition. Consequently, the corresponding stored elastic energy in the inclusion is released through the inclusion-host boundary into the host matrix while crossing the α–β transition, causing the garnet around the quartz inclusion to fracture or even, in some cases, shatter due to the large differential stresses developing in the inclusion at its transition. Inclusions of apatite and zircon in the same garnets remain unchanged at the same conditions, excluding the fracturing being caused by the host garnet itself.We propose that this process can create sufficient fracturing in lower–crustal garnets, which can in turn accumulate into planar fractures along garnet-rich layers and thus trigger brittle failure and seismicity.ReferencesLakshtanov, D.L., Sinogeikin, S.V., Bass, J.D., 2007. High-temperature phase transitions and elasticity of silica polymorphs. Physics and Chemistry of Minerals 34, 11-22.

The templating role in the formation of 2D metal halide perovskites of diammonium cations, such as 1,3-phenylenediammonium, 1,3-xylylenediammonium, 1,4-phenylenediammonium, and 1,4-xylylenediammonium cations, has been investigated.

There is increasing interest in the role of metal halide perovskites for heterogeneous catalysis. Here, we report a Ge-based 2D perovskite material that shows intrinsic water stability realized through organic cation engineering. Incorporating 4-phenylbenzilammonium (PhBz) we demonstrate, by means of extended experimental and computational results, that PhBz2GeBr4 and PhBz2GeI4 can achieve relevant air and water stability. The creation of composites embedding graphitic carbon nitride (g-C3N4) allows a proof of concept for light-induced hydrogen evolution in an aqueous environment by 2D Ge-based perovskites thanks to the effective charge transfer at the heterojunction between the two semiconductors.

We report here the preparation and characterization of two families of RP 2D perovskites including linear monoammonium cations, namely (CnH2n+1NH3)2PbBr4 and (CnH2n+1NH3)2PbI4 with n=4, 6, 8, 10, 12, 14 and 16. Structural and optical properties shows some similarities between the two series of samples with, however, distinct features related to the presence of phase transitions occurring when different ligands are present. Optical properties confirm a general blue-shift for the (CnH2n+1NH3)2PbBr4 system with respect to the (CnH2n+1NH3)2PbI4 family with the PL data showing two distinct variation paths for their excitonic emission behavior, one directly related to the chain length and another one depending on the ammonium coordination to the halogen atoms. Water stability of (CnH2n+1NH3)2PbBr4 and (CnH2n+1NH3)2PbI4 has been assessed and the results show an improved hydrophobicity by increasing the number of carbon atoms of the alkyl chain as well as by moving from iodide to bromide perovskites.

The role of templating the formation of 2D metal halide perovskites has been investigated by considering the 1,3-phenylenediammonium (1,3-PDA), 1,3-xylylenediamimonium (1,3-XDA), 1,4-phenylenediammonium (1,4-PDA), and 1,4-xylylenediamimonium (1,4-XDA) cations in lead bromide systems. Single-crystal x-ray diffraction confirms the formation 2D Dion-Jacobons (DJ) perovskites for all the cations except for the 1,3-XDA cation leading to a so-called 0D perovskitoid. Analysis of the structural data showed a higher distortion degree for the systems containing the shorter cation, namely 1,4-PDA. A detailed spectroscopic investigation, with both static and time resolved photoluminescence spectroscopy, revealed a broadband emissive component at room temperature with hundreds of nanometers of bandwidth when 1,3-PDA and 1,4-PDA cations are present, while a narrow peak is found for the longer cation, i.e. 1,4-XDA. A broadband emission arises in this last sample as well by decreasing temperature. Such broad emission, as indicated by the analysis of the power and temperature dependence of the PL, can be attributed to trap-mediated excitonic recombination or STEs, and the trend in emissive properties can be correlated to the different level of octahedral distortions. The novel systems reported in this work enlarge the family of broadband emitters and add further clues to develop efficient perovskite-based broadband and white light emitters.

The role of halide substitution in a lead-free 2D hybrid perovskite is investigated on the BZA(2)SnX(4) (BZA = benzylammonium; X = Cl, Br and I) system, by reporting the synthesis and the structural analysis by means of single-crystal X-ray diffraction data of the two novel compositions BZA(2)SnBr(4) and BZA(2)SnCl(4). In addition, the mixed composition BZA(2)Sn(BrxI1-x)(4) (0

Tin halide perovskites have the potential to overcome the toxicity issues of lead-based systems for photovoltaic devices. Elucidation of local structural features in these systems is of fundamental relevance to better understand the optoelectronic properties. This has been realized in ASnX3 (A= MA, FA, and X= I, Br) by total scattering and X-ray pair distribution function analysis, showing a trend of increasing local distortion as a function of organic cation, halide and temperature.

The application of an external pressure on Metal Halide Perovskite (MHPs) has become a fascinating way of tuning their optical properties, achieving also novel features. Here, the pressure response of 2D MHPs including a long alkyl chain made of ten carbon atoms, namely decylammonium (DA), has been investigated as a function of the central atom in DA2PbI4 and DA2GeI4. The two systems share a common trend in the phase stability, displaying a transition from an orthorhombic to a monoclinic phase around 2 GPa, followed by a phase separation in two monoclinic phases characterized by different c-axis. The optical properties show rather different behavior due to the presence of Pb or Ge. DA2PbI4 shows a progressive red shift of the band gap from 2.28 eV at ambient conditions, to 1.64 eV at 11.5 GPa, with a narrow PL emission composed by two components, with the second one appearing in concomitance with the phase separation and significantly shifted to lower energy. On the other hand, DA2GeI4, changes from a non-PL system at ambient pressure, to a clear broadband emitter centered around 730 nm (FWHM ~ 170 nm), with a large stoke shift, and an intensity maximum at about 3.7 GPa. This work sheds light on the structural stability of 2D perovskites characterized by extended alkyl chains, to date limited to four carbon atoms, and shows the pressure-induced emergence of broad emission in a novel lead-free perovskite, DA2GeI4. The evidence of wide emission by a moderate pressure in a germanium-based 2D MHP represents a novel result which may open the design, by chemical pressure, of efficient wide or even white lead-free emitters.

Manipulation by external pressure of the optical response of 2D Metal Halide Perovskites (MHPs) is a fascinating route to tune their properties and promote the emergence of novel features. We investigate here DA

Chemical reactivity between As and N2 , leading to the synthesis of crystalline arsenic nitride, is here reported under high pressure and high temperature conditions generated by laser heating in a Diamond Anvil Cell. Single crystal synchrotron X-ray diffraction at different pressures between 30 and 40 GPa provides evidence for the synthesis of a covalent compound of AsN stoichiometry, crystallizing in a cubic P213 space group, in which each of the two elements is single-bonded to three atoms of the other and hosts an electron lone pair, in a tetrahedral anisotropic coordination. The identification of characteristic structural motifs highlights the key role played by the directional repulsive interactions between non-bonding electron lone pairs in the formation of the AsN structure. Additional data indicate the existence of AsN at room temperature from 9.8 up to 50 GPa. Implications concern fundamental aspects of pnictogens chemistry and the synthesis of innovative advanced materials.

Perovskites are attracting an increasing interest in the wide community of photovoltaics, optoelectronic, and detection, traditionally relying on lead-based systems. This Minireview provides an overview of the current status of experimental and computational results available on Ge-containing 3D and low-dimensional halide perovskites. While stability issues analogous to those of tin-based materials are present, some strategies to afford this problem in Ge metal halide perovskites (MHPs) for photovoltaics have already been identified and successfully employed, reaching efficiencies of solar devices greater than 7 % at up to 500 h of illumination. Interestingly, some Ge-containing MHPs showed promising nonlinear optical responses as well as quite broad emissions, which are worthy of further investigation starting from the basic materials chemistry perspective, where a large space for properties modulation through compositions/alloying/fnanostructuring is present.

Spryite (Ag7.98Cu0.05)Σ=8.03(As5+0.31Ge0.36As3+0.31Fe3+0.02)Σ=1.00S5.97, and ideally Ag8(As3+0.5As5+0.5)S6, is a new mineral recently described from the Uchucchacua polymetallic deposit, Oyon district, Catajambo, Lima Department, Peru. Its room temperature structure exhibits an orthorhombic symmetry, space group Pna21, with lattice parameters a = 14.984(4), b = 7.474(1), c = 10.571(2) Å, V = 1083.9(4) Å3, Z = 4, and shows the coexistence of As3+ and As5+ distributed in a disordered fashion in a unique mixed position. To analyze the crystal-chemical behaviour of the arsenic distribution at ultra-low temperatures, a structural study was carried out at 30 K by means of in situ single-crystal X-ray diffraction data (helium-cryostat) on the same sample previously characterized from a chemical and structural point of view. At 30 K, spryite still crystallizes with orthorhombic symmetry, space group Pna21, but gives rise to a a × 3b × c superstructure, with a = 14.866(2), b = 22.240(4), c = 10.394(1) Å, V = 3436.5(8) Å3 and Z = 4 (Ag24As3+As5+Ge4+S18 stoichiometry). The twin laws making the twin lattice simulating a perfect hexagonal symmetry have been taken into account and the crystal structure has been solved and refined. The refinement of the structure leads to a residual factor R = 0.0329 for 4070 independent observed reflections [with Fo &gt, 4σ(Fo)] and 408 variables. The threefold superstructure arises from the ordering of As3+ and (As5+, Ge4+) in different crystal-chemical environments.

The insertion of oxygen and nitrogen molecules in the one-dimensional (1D) pore system of the zeolite TON was studied at high pressure by vibrational spectroscopy, X-ray diffraction, and Monte Carlo (MC) molecular modeling. Rietveld refinements and MC modeling indicate that, on average, six diatomic molecules per unit cell enter the pores of the zeolite. This induces changes in compressibility and distortion related to the Cmc21-to-Pbn21 phase transition compared to the empty-pore material. The filling behavior with N2 and O2 under pressure is similar to that of argon, suggesting that the kinetic diameter, which is very close in these three systems, plays a major role. The orientation of the diatomic molecules appears to have a rather minor effect on filling occurring at a slightly higher pressure for N2, which has a larger kinetic diameter. Both inserted molecules, initially not showing any marked orientation, begin to exhibit a degree of orientational order above 2 GPa.

The elucidation of the structure–property correlation in 2D metal halide perovskite is a key issue to understand the dependence of optical properties on structural distortions and to design novel tailored materials. To extend the actual knowledge on this kind of correlation for lead-free materials, here we report four novel 2D germanium bromide perovskites, namely A2GeBr4with A = phenylethylammonium, PEA, Br-phenylethylammonium, BrPEA, F-phenylethylammonium, FPEA, and benzylammonium BZA. A dependence of the band gap value and emission characteristics in terms of Stokes shift and peak width has been highlighted and correlated with the octahedral distortion parameters. In addition, by comparing the actual results with previous data on analogous Sn- and Pb-based materials, we observed an intrinsic increased distortion induced by germanium, particularly on the octahedral bond elongation and bond angle variance, and less on the Ge–Br–Ge bond angle. The structural and optical investigation, together with density functional theory simulations, clarified the role of different structural distortion parameters on the optical properties for a series of 2D Ge-containing perovskites, thus providing novel clues for the future design of layered lead-free materials.

The pressure dependence of the polarized Raman scattering of quartz was studied under hydrostatic conditions up to 9 GPa. We extended the available pressure calibrations, usually limited to the two most intense peaks, to a larger number of modes, providing polynomial functions that describe the relationship between pressure P and wavenumber shift $$\Delta \omega$$ for the 128-, 206-, 265-, 464-, 696-, 809-, 1080- and 1161- $$\hbox {cm}^{-1}$$ modes. For the first time, the pressure behavior of the LO-TO splitting is characterized up to 9 GPa under hydrostatic conditions. The pressure-induced wavenumber changes and derived phonon compressibilities show that longitudinal and transverse modes can be used interchangeably for the calculation of strains through the Gruneisen tensor to derive the strains in crystals, such as mineral inclusions, under non-hydrostatic conditions. A careful examination of the linewidths as a function of pressure shows that they are sensitive to the metastability of the quartz structure with respect to the high-pressure silica polymorphs. It is proposed that strong multiphonon interactions contribute to the stability of the structure of quartz at ambient conditions.

Investigation of mantle xenoliths can provide information on the architecture and evolution of subcontinental lithospheric mantle through time. These reconstructions rely also on correct estimates of the pressures and temperatures (P-T) experienced by these rocks over time. Unlike chemical geothermobarometers, elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide information on over-stepping of reaction boundaries and to identify other examples of non-equilibrium behaviour in rocks. Here we introduce a method that exploits the elastic anisotropy of minerals to determine the unique P and T of equilibration from a measurements of single-crystal mineral inclusions trapped in a crystalline host from an eclogite xenolith [1]. We apply it to perfectly preserved quartz inclusions in garnet from eclogite xenoliths in kimberlites. We show that the elastic strains of inclusions calculated from in-house Raman spectroscopy measurements of the inclusions are in perfect agreement with those determined from in-situ X-ray diffraction measurements performed both in-house and at the synchrotron. Calculations based on these measured strains demonstrate that quartz trapped in garnet can be preserved even when the rock passes into the stability field of coesite (high pressure and temperature polymorph of quartz). This supports a metamorphic origin for these xenoliths that provides constraints on mechanisms of craton accretion from a subducted crustal protolith. Furthermore, we show that some key inclusion minerals do not always indicate the P and T attained during subduction and metamorphism. This project has received funding from the European Research Council under the H2020 research and innovation programme (N. 714936 TRUE DEPTHS to M. Alvaro) [1] M Alvaro, ML Mazzucchelli, RJ Angel, M Murri, N Campomenosi, M Scambelluri, F Nestola, A Korsakov, AA Tomilenko, F Marone, M Morana (2020) Fossil subduction recorded by quartz from the coesite stability field, Geology, 48, 24-28

International audience; Condensed O2 tends to form clusters, even with a long-range order. In particular, in solid oxygen, strong intermolecular charge transfer at high pressures leads to the formation of (O2)4 tetramers above 10 GPa, in the ε-O2 phase, with weak O2–O2 chemical bonds. Indeed, ε-O2 is entirely made of these tetramers. We conducted experimental investigations on strongly densified O2 in a different environment, that is to say in the form of a subnano phase build up within the 1D microchannels of a purely siliceous, inert zeolite, TON, at pressures of 0.5–20 GPa, by means of diamond anvil cells. Our X-ray diffraction and infrared and Raman spectroscopy results consistently show that oxygen forms clusters in this nanophase, above 10 GPa, similar to ε-O2, except that the clusters are rather of the type of weakly bonded (O2)2 dimers in this case. Also, by analogy with bulk oxygen, we show that the O2 spin within the dimers departs from S = 1 toward lower values, upon increasing pressure. Our findings thereby add to the general view on essential properties of highly dense oxygen.

Here we describe a new mineral in the Cu-Ag-Te system, spiridonovite. The specimen was discovered in a fragment from the cameronite [ideally, Cu5-x(Cu,Ag)3+xTe10] holotype material from the Good Hope mine, Vulcan, Colorado (U.S.A.). It occurs as black grains of subhedral to anhedral morphology, with a maximum size up to 65 &mu, m, and shows black streaks. No cleavage is observed and the Vickers hardness (VHN100) is 158 kg&middot, mm-2. Reflectance percentages in air for Rmin and Rmax are 38.1, 38.9 (471.1 nm), 36.5, 37.3 (548.3 nm), 35.8, 36.5 (586.6 nm), 34.7, 35.4 (652.3 nm). Spiridonovite has formula (Cu1.24Ag0.75)&Sigma, 1.99Te1.01, ideally (Cu1-xAgx)2Te (x &asymp, 0.4). The mineral is trigonal and belongs to the space group P-3c1, with the following unit-cell parameters: a = 4.630(2) &Aring, c = 22.551(9) &Aring, V = 418.7(4) &Aring, 3, and Z = 6. The crystal structure has been solved and refined to R1 = 0.0256. It can be described as a rhombohedrally-compressed antifluorite structure, with a rough ccp arrangement of Te atoms. It consists of two Te sites and three M (metal) sites, occupied by Cu and Ag, and is characterized by the presence of edge-sharing tetrahedra, where the four-fold coordinated M atoms lie. The mineral and its name have been approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (No. 2018-136).

We report data on the composition and crystal structure of the first As3+-bearing natural argyrodite, spryite. Spryite has the formula $$({{\text{Ag}}_{7.98} {\text{Cu}}_{0.05}})_{\varSigma = 8.03} ({{\text{As}}_{0.31}^{5 +} {\text{Ge}}_{0.36} {\text{As}}_{0.31}^{3 +} {\text{Fe}}_{0.02}^{3 +}})_{\varSigma = 1.00} {\text{S}}_{5.97}$$ , ideally $${\text{Ag}}_{8} ({{\text{As}}_{0.5}^{3 +} {\text{As}}_{0.5}^{5 +}}){\text{S}}_{6}$$ . The crystal studied was found in a sample from the Uchucchacua polymetallic deposit, Oyon district, Cajatambo, Lima Department, Peru. The structure was refined in the space group Pna21 up to R = 0.0782 using 2099 observed reflections [2σ(I) level]. Spryite is intimately twinned with six twin domains. The structure solution showed that As3+ and As5+ coexist in the new mineral, which represents the first case ever discovered in either a mineral or a synthetic compound belonging to a sulfide/sulfosalt group. High-temperature in situ X-ray diffraction experiments indicated that no phase transitions occur in the temperature range investigated and that the mineral does not show any evidence of fast ionic conduction.

Magnetic mineral inclusions, as iron oxides or sulfides, occur quite rarely in natural diamonds. Nonetheless, they represent a key tool not only to unveil the conditions of formation of host diamonds, but also to get hints about the paleointensity of the geomagnetic field present at times of the Earth's history otherwise not accessible. This possibility is related to their capability to carry a remanent magnetization dependent on their magnetic history. However, comprehensive experimental studies on magnetic inclusions in diamonds have been rarely reported so far. Here we exploit X-ray diffraction, Synchrotron-based X-ray Tomographic Microscopy and Alternating Field Magnetometry to determine the crystallographic, morphological and magnetic properties of ferrimagnetic Fe-oxides entrapped in diamonds coming from Akwatia (Ghana). We exploit the methodology to estimate the natural remanence of the inclusions, associated to the Earth's magnetic field they experienced, and to get insights on the relative time of formation between host and inclusion systems. Furthermore, from the hysteresis loops and First Order Reversal Curves we determine qualitatively the anisotropy, size and domain state configuration of the magnetic grains constituting the inclusions., v1: PDFLaTeX,12 pages,9 figs,1 table; v2: PDFLaTeX,10 pages,8 figs,1 table. All sections reorganized and shortened; some references deleted; Introduction and Discussion sections clarified; Figs. 4,5 of version v1 merged in new-Fig. 4; typos corrected; v3: PDFLaTeX,10 pages,8 figs,1 table. Slight changes in Introduction; few typos corrected. Accepted for publication in Diamond and Related Materials

Metamorphic rocks are the records of plate tectonic processes whose reconstruction relies on correct estimates of the pressures and temperatures (P-T) experienced by these rocks through time. Unlike chemical geothermobarometry, elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide information on overstepping of reaction boundaries and to identify other examples of non-equilibrium behavior in rocks. Here we introduce a method that exploits the anisotropy in elastic properties of minerals to determine the unique P and T of entrapment from a single inclusion in a mineral host. We apply it to preserved quartz inclusions in garnet from eclogite xenoliths hosted in Yakutian kimberlites (Russia). Our results demonstrate that quartz trapped in garnet can be preserved when the rock reaches the stability field of coesite (the high-pressure and high-temperature polymorph of quartz) at 3 GPa and 850 °C. This supports a metamorphic origin for these xenoliths and sheds light on the mechanisms of craton accretion from a subducted crustal protolith. Furthermore, we show that interpreting P and T conditions reached by a rock from the simple phase identification of key inclusion minerals can be misleading.