The P-T phase diagram of the hydrated magnesium carbonate nesquehonite (MgCO₃·3H₂O) has not been reported in the literature. In this paper, we present a joint experimental and computational study of the phase stability and structural behavior of this cementitious material at high-pressure and high-temperature conditions using in situ single-crystal and synchrotron powder X-ray diffraction measurements in resistive-heated diamond anvil cells plus density functional theory calculations. Our results show that nesquehonite undergoes two pressure-induced phase transitions at 2.4 (HP1) and 4.0 GPa (HP2) at ambient temperature. We have found negative axial compressibility and thermal expansivity values, likely related to the directionality of the hydrogen bonds. The equations of state of the different phases have been determined. All the room-temperature compression effects were reversible. Heating experiments at 0.7 GPa show a first temperature-induced decomposition at 115 °C, probably into magnesite and a MgCO₃·4H₂O phase.

Time-correlated single photon counting has been conducted to gain further insights into the short photoluminescence lifetimes (nanosecond) of lead iodide perovskite (MAPbI₃) thin films (∼100 nm). We analyze three different morphologies, compact layer, isolated island, and connected large grain films, from 14 to 300 K using a laser excitation power of 370 nJ/cm². Lifetime fittings from the Generalized Berberan-Santos decay model range from 0.5 to 6.5 ns, pointing to quasi-direct bandgap emission despite the three different sample strains. The high energy band emission for the isolated-island morphology shows fast recombination rate centers up to 4.8 ns^–1, compared to the less than 2 ns^–1 for the other two morphologies, similar to that expected in a good quality single crystal of MAPbI₃. Low-temperature measurements on samples reflect a huge oscillator strength in this material where the free exciton recombination dominates, explaining the fast lifetimes, the low thermal excitation, and the thermal escape obtained.

Given the seriousness of the socio-environmental situation we are facing, this study aims to contribute to the involvement of teachers in education for sustainability through the use of non-formal education, particularly the press. The main objectives of the present study are to analyse the use of the press in science education, as well as the design, implementation and evaluation of tools aimed at teachers and trainee researchers in order to encourage and promote attention to the Sustainable Development Goals (SDGs) and more specifically SDG 7 (clean and affordable energy for all) in science education. The proposals are carried out using a constructivist methodology in sessions structured in small collaborative groups. The initial results show that attention to the press is still insufficient, but that, nevertheless, the strategies designed contribute to raising awareness of the importance of SDG 7 and to the classroom treatment of the energy issue among the participants in the study who attend a Master’s degree program in secondary education teacher training (specialising in physics and chemistry) and a Master’s degree program in research in specific didactics (specialising in experimental sciences).

We report the experimental high-pressure crystal structure and equation of state of gold(I) sulfide (Au₂S) determined using diamond-anvil cell synchrotron X-ray diffraction. Our data shows that Au₂S has a simple cubic structure with six atoms in the unit cell (four Au in linear, and two S in tetrahedral, coordination), no internal degrees of freedom, and relatively low bulk modulus. Despite its structural simplicity, Au₂S displays very unusual chemical bonding. The very similar and relatively high electronegativities of Au and S rule out any significant metallic or ionic character. Using a simple valence bond (Lewis) model, we argue that the Au₂S crystal possesses two different types of covalent bonds: dative and shared. These bonds are distributed in such a way that each Au atom engages in one bond of each kind. The multiple arrangements in space of dative and shared bonds are degenerate, and the multiplicity of configurations imparts the system with multireference character, which is highly unusual for an extended solid. The other striking feature of this system is that common computational (DFT) methods fail quite spectacularly to describe it, with 20% and 400% errors in the equilibrium volume and bulk modulus, respectively. We explain this by the poor treatment of static correlation in common density-functional approximations. The fact that the solid is structurally very simple, yet presents unique chemical bonding and is unmodelable using current DFT methods, makes it an interesting case study and a computational challenge.

New single-crystal X-ray diffraction experiments and density functional theory (DFT) calculations reveal that the crystal chemistry of the CaO–BaO–CO₂ system is more complex than previously thought. We characterized the BaCa(CO₃)₂ alstonite structure at ambient conditions, which differs from the recently reported crystal structure of this mineral in the stacking of the carbonate groups. This structural change entails the existence of different cation coordination environments. The structural behavior of alstonite at high pressures was studied using synchrotron powder X-ray diffraction data and ab initio calculations up to 19 and 50 GPa, respectively. According to the experiments, above 9 GPa, the alstonite structure distorts into a monoclinic C2 phase derived from the initial trigonal structure. This is consistent with the appearance of imaginary frequencies and geometry relaxation in DFT calculations. Moreover, calculations predict a second phase transition at 24 GPa, which would cause the increase in the coordination number of Ba atoms from 10 to 11 and 12. We determined the equation of state of alstonite (V₀ = 1608(2) ų, B₀ = 60(3) GPa, B′₀ = 4.4(8) from experimental data) and analyzed the evolution of the polyhedral units under compression. The crystal chemistry of alstonite was compared to that of other carbonates and the relative stability of all known BaCa(CO₃)₂ polymorphs was investigated.

The structure of the naturally occurring, iron-rich mineral Ca_1.08(6)Mg_0.24(2)Fe_0.64(4)Mn_0.04(1)(CO₃)₂ ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch–Murnaghan equation of state yields V₀ = 328.2(3) ų, bulk modulus B₀ = 89(4) GPa, and its first-pressure derivative B’₀ = 5.3(8)—values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO₃)₂ ankerite composition. At 12 GPa, the iron-rich ankerite structure undergoes a reversible phase transition that could be a consequence of increasingly non-hydrostatic conditions above 10 GPa. The high-pressure phase could not be characterized. DFT calculations were used to explore the relative stability of several potential high-pressure phases (dolomite-II-, dolomite-III- and dolomite-V-type structures), and suggest that the dolomite-V phase is the thermodynamically stable phase above 5 GPa. A novel high-pressure polymorph more stable than the dolomite-III-type phase for ideal CaFe(CO₃)₂ ankerite was also proposed. This high-pressure phase consists of Fe and Ca atoms in sevenfold and ninefold coordination, respectively, while carbonate groups remain in a trigonal planar configuration. This phase could be a candidate structure for dense carbonates in other compositional systems.