Structural and vibrational characterization of vanadate materials under high pressure conditions based on experimental analysis
- Autores: Josu Sánchez Martín
- Directores de la Tesis: Julio Pellicer Porres (dir. tes.), Daniel Errandonea (codir. tes.)
- Lectura: En la Universitat de València ( España ) en 2025
- Idioma: inglés
- Número de páginas: 159
- Tribunal Calificador de la Tesis: Fernando Rodríguez González (presid.), David Santamaria-Perez (secret.), Silvia Boccato (voc.)
- Programa de doctorado: Doctor en Programa Oficial de Posgrado en Física
- Materias:
- Enlaces
- Resumen
The rich polymorphism and physical properties of the vanadate compounds have attracted the attention of the high-pressure scientific community for many decades. This thesis synthesizes the findings from a series of experiments conducted on eight distinct vanadate materials. These materials belong to various subfamilies and have demonstrated noteworthy results.
Trivalent metal orthovanadates are recognized for their abundant and highly systematic phase diagram. Four phases of BiVO4 have been studied under high-pressure and high-temperature, upgrading the substantial literature around this compound. In the case of ErVO4, the zircon-scheelite phase transition has been thoroughly studied, which has confirmed that it is indeed a process without phase coexistence when highly hydrostatic conditions and single-crystal samples are employed. Three other divalent metal orthovanadates were also studied. Whitlockite-type Ca3V2O8 underwent a non-hydrostatic induced phase transition to a monoclinic structure at 9.8 GPa. Conversely, Ni3V2O8 and Co3V2O8 were compared from the vibrational perspective as both preserved the same orthorhombic structure up to 20 GPa. Two special cases of the metavanadate subfamily were investigated. The distinctive orthorhombic structure of PbV2O6 presented nearly zero linear compressibility of its b-axis, and also a coordination increase of the VO5 polyhedra to a VO6 octahedra around 5 GPa. The pressure-synthesized columbite-type CoV2O6 presented two phase transitions up to 50 GPa, the first one at 20 GPa being isostructural and the second one to a monoclinic distortion at around 45 GPa, both identified in single-crystal XRD and Raman experiments. The spinel FeV2O4 presented reversible pressure-induced chemical decomposition at 12 GPa into FeO and V2O3 subproducts, which were previously present in the powder sample.
Most of the results are supported by density-functional calculations, as the published articles included in the text demonstrate. A detailed review of the experimental and subsequent analysis procedure explanation is included in the thesis. The final discussion section connects the different vanadates from four important perspectives of the high-pressure physics field; namely the impurities in the sample, phase transitions, pressure coefficient properties and symmetry assignation of the Raman modes.
