Persistent spin dynamics in the pressurized spin-liquid candidate YbMgGaO4_4

Single-crystal x-ray diffraction, density-functional band-structure calculations, and muon spin relaxation ($\mu$SR) are used to probe pressure evolution of the triangular spin-liquid candidate YbMgGaO$_4$. The rhombohedral crystal structure is retained up to at least 10 GPa and shows a nearly uniform compression along both in-plane and out-of-plane directions, whereas local distortions caused by the random distribution of Mg$^{2+}$ and Ga$^{3+}$ remain mostly unchanged. The $\mu$SR data confirm persistent spin dynamics up to 2.6 GPa and down to 250 mK with no change in the muon relaxation rate. Longitudinal-field $\mu$SR reveals power-law behavior of the spin-spin autocorrelation function, both at ambient pressure and upon compression.Comment: published versio

Enhancing the chemical flexibility of hybrid perovskites by introducing divalent ligands

Herein we report the synthesis and structures of [(CH$_3$)$_2$NH$_2$]Er(HCO$_2$)$_2$(C$_2$O$_4$) and [(NH$_2$)$_3$C]Er(HCO$_2$)$_2$(C$_2$O$_4$), in which the inclusion of divalent oxalate ligands allows for the exclusive incorporation of A$^+$ and B$^{3+}$ cations in an ABX$_3$ hybrid perovskite structure for the first time. We rationalise the observed thermal expansion of these materials, including negative thermal expansion, and find evidence for weak antiferromagnetic coupling in [(CH$_3$)$_2$NH$_2$]Er(HCO$_2$)$_2$(C$_2$O$_4$)

Polymorphism in M(H2PO2)3 (M = V, Al, Ga) compounds with the perovskite-related ReO3 structure.

Trivalent metal hypophosphites with the general formula M(H2PO2)3 (M = V, Al, Ga) adopt the ReO3 structure, with each compound displaying two structural polymorphs. High-pressure synchrotron X-ray studies reveal a pressure-driven phase transition in Ga(H2PO2)3 that can be understood on the basis of ab initio thermodynamics

Complete Set of Elastic Moduli of a Spin-Crossover Solid: Spin-State Dependence and Mechanical Actuation

Molecular spin crossover complexes are promising candidates for mechanical actuation purposes. The relationships between their crystal structure and mechanical properties remain, however, not well understood. In this study, combining high pressure synchrotron Xray diffraction and nuclear inelastic scattering measurements, we assessed the effective macroscopic bulk modulus (11.5 ± 2.0 GPa), Young’s modulus (10.9 ± 1.0 GPa) and Poisson’s ratio (0.34 ± 0.04) of the spin crossover complex [FeII(HB(tz)3)2] (tz = 1,2,4-triazol-1-yl) in its low spin state. Crystal structure analysis revealed a pronounced anisotropy of the lattice compressibility, which was correlated with the difference in spacing between the molecules in different crystallographic directions. Switching the molecules from the low spin to the high spin state leads to a remarkable drop of the Young’s modulus to 7.1 ± 0.5 GPa, which was also assessed in thin film samples by means of micromechanical measurements. These results are in agreement with the high cooperativity of the spin crossover in this compound and highlight its application potential in terms of recoverable stress (21 ± 1 MPa) and work density (15 ± 6 mJ/cm3)

Packing Rearrangements in 4-Hydroxycyanobenzene Under Pressure

4-hydroxycyanobenzene (4HCB) is a dipolar molecule formed of an aromatic substituted benzene ring with the CN and OH functional groups at the 1 and 4 positions. In the crystalline state, it forms spiral chains via hydrogen bonding, which pack together through π − π interactions. The direct stacking of benzene rings down the a- and b-axes and its π − π interactions throughout the structure gives rise to its semiconductor properties. Here, high-pressure studies are conducted on 4HCB in order to investigate how the packing and intermolecular interactions, related to its semiconductor properties, are affected. High-pressure single-crystal X-ray diffraction was performed with helium and neon as the pressure-transmitting mediums up to 26 and 15 GPa, respectively. The pressure-dependent behaviour of 4HCB in He was dominated by the insertion of He into the structure after 2.4 GPa, giving rise to two phase transitions, and alterations in the π − π interactions above 4 GPa. 4HCB compressed in Ne displayed two phase transitions associated with changes in the orientation of the 4HCB molecules, giving rise to twice as many face-to-face packing of the benzene rings down the b-axis, which could allow for greater charge mobility. In the He loading, the hydrogen bonding interactions steadily decrease without any large deviations, while in the Ne loading, the change in 4HCB orientation causes an increase in the hydrogen bonding interaction distance. Our study highlights how the molecular packing and π − π interactions evolve with pressure as well as with He insertion