Polymorphism and Phase Stability of Hydrated Magnesium Carbonate Nesquehonite MgCO·3HO: Negative Axial Compressibility and Thermal Expansion in a Cementitious Material.

The - phase diagram of the hydrated magnesium carbonate nesquehonite (MgCO·3HO) 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 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.

Structural Behavior of Minrecordite Carbonate Mineral upon Compression: Effect of Mg → Zn Chemical Substitution in Dolomite-Type Compounds.

We report the structural behavior and compressibility of minrecordite, a naturally occurring Zn-rich dolomite mineral, determined using diamond-anvil cell synchrotron X-ray diffraction. Our data show that this rhombohedral CaZnMg(CO) carbonate exhibits a highly anisotropic behavior, the axis being 3.3 times more compressible than the axis.

Phase stability and dense polymorph of the BaCa(CO) barytocalcite carbonate.

The double carbonate BaCa(CO) holds potential as host compound for carbon in the Earth's crust and mantle. Here, we report the crystal structure determination of a high-pressure BaCa(CO) phase characterized by single-crystal X-ray diffraction. This phase, named post-barytocalcite, was obtained at 5.

Short Photoluminescence Lifetimes Linked to Crystallite Dimensions, Connectivity, and Perovskite Crystal Phases.

Time-correlated single photon counting has been conducted to gain further insights into the short photoluminescence lifetimes (nanosecond) of lead iodide perovskite (MAPbI) 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/cm. Lifetime fittings from the Generalized Berberan-Santos decay model range from 0.

Crystal Structure of BaCa(CO) Alstonite Carbonate and Its Phase Stability upon Compression.

New single-crystal X-ray diffraction experiments and density functional theory (DFT) calculations reveal that the crystal chemistry of the CaO-BaO-CO system is more complex than previously thought. We characterized the BaCa(CO) 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.