arXiv subjects

Josu Sanchez-Martin

Publications and source records attributed to Josu Sanchez-Martin.

4 recordsLinked to original sources

arXiv2026

Effects of Compression on the Local Iodine Environment in Dipotassium Zinc Tetraiodate(V) Dihydrate K2Zn(IO3)4.2H2O

Combining X-ray diffraction with density-functional theory and electron topology calculations we found that pressure substantially modifies the bonding in K2Zn(IO3)4.2H2O. We discovered that under compression there is a progressive change from primary covalent I-O bonds and secondary halogen I-O interactions towards O-I-O electron-deficient multicenter bonds. Because of this, iodine hypercoordination converts IO3 trigonal pyramids towards IO6 units. The formation of these IO6 units breaks the typical isolation of iodate molecules forming an infinite two-dimensional iodate network. Hypercoordination influences the hydrogen atoms too, such that multicenter O-H-O bonds are also promoted with increasing pressure. We have determined that K2Zn(IO3)4.2H2O is one of the most compressible iodates studied to date, with a bulk modulus of 22(3) GPa. The pressure-induced structural changes strongly modify the electronic structure as shown by optical-absorption measurements and band-structure calculations. The band-gap energy closes from 4.2(1) eV at ambient pressure to 3.4(1) eV at 20 GPa.

cond-mat.mtrl-sci↗

arXiv2026

High-pressure single-crystal X-ray diffraction study of ErVO4

We present an investigation into the crystal structure of ErVO4 under variable pressure conditions. The high-pressure single crystal X-ray diffraction experiments performed employing helium as the pressure medium facilitated structure refinements up to 24.1(2) GPa. The transition from zircon to scheelite was observed at a pressure of 7.9(1) GPa. In contrast to previous reports, we did not detect any sign of phase coexistence. We also did not observe the second phase transitions previously predicted by density-functional theory to occur below 20 GPa. The determination of the pressure dependence of unit-cell parameters and volume yields precise values for linear compressibility of each axis and the pressure-volume equation of state for both the zircon and scheelite phases. Additional information on the mechanical properties of ErVO4, obtained from density-functional theory calculations, is also reported.

cond-mat.mtrl-sci↗

arXiv2026

High-Pressure X-Ray Diffraction Study of Scheelite-type Perrhenates

The effects of pressure on the crystal structure of scheelite-type perrhenates were studied using synchrotron powder X-ray diffraction and density-functional theory. At ambient conditions, the studied materials AgReO4, KReO4, and RbReO4, exhibit a tetragonal scheelite-type crystal structure described by space group I41/a. Under compression, a transition from scheelite-to-M${\prime}$-fergusonite (space group P21/c) was observed at 1.6 and 7.4 GPa for RbReO4 and KReO4, respectively. The transition involves a relative volume decrease. On the other hand, AgReO4 underwent a phase transition to the M-fergusonite structure (space group I2/a) at 13.6 GPa. In this case there is no appreciable volume discontinuity. The room-temperature pressure-volume equation of state for the three studied perrhenates was estimated using a second-order Birch-Murnaghan equation of state. The results for the low-pressure phase are confirmed by density-functional theory calculations. The analysis of the bulk modulus shows that the compressibility of the compounds decreases following the sequence RbReO4 > KReO4 > AgReO4, which is related to the compressibility of the RbO8, KO8, and AgO8 bidisphenoid units. Density-functional theory also offers valuable insights into the elastic constants. Despite giving a good description for the low-pressure phase in the three compounds, density-functional theory cannot catch the structural phase transition observed in experiments. Reasons for it are discussed in the manuscript.

cond-mat.mtrl-sci↗

arXiv2025

A comparative study of the high-pressure structural stability of zirconolite materials for nuclear waste immobilisation

We present a comparative study of the high-pressure behaviours of the nuclear waste immobilisation materials zirconolite-2M, -4M, -3O, and -3T. The materials are studied under high-pressure conditions using synchrotron powder X-ray diffraction. For zirconolite-2M we also performed density-functional theory calculations. A new triclinic crystal structure (space group P-1), instead of the previously assigned monoclinic structure (space group C2/c) is proposed for zirconolite-2M. We named the triclinic structure as zirconolite-2TR. We also found that zirconolite-2TR undergoes a phase transition at 14.7 GPa to a monoclinic structure described by space group C2/c, which is different than the high-pressure structure previously proposed in the literature. These results are discussed in comparison with previous studies on zirconolite-2M and the related compound calzirtite. For the other three zirconolite structures (4M, 3O, and 3T) this is the first high-pressure study, and we find no evidence for pressure induced phase transitions in any of them. The linear compressibility of the studied compounds, as well as a room-temperature pressure-volume equation of state, are also presented and discussed.

cond-mat.mtrl-sci↗