Fingerprints of short-range and long-range structure in BaZr_1−xHf_xO₃ solid solutions: an experimental and theoretical study

Abstract

Microwave-assisted hydrothermal method was applied to synthesize BaZr 1−x Hf x O 3 , (BZHO) solid solutions at low temperature, 140 • C, and relative short times, 160 min. The detailed features of the crystal structure, at both short and long ranges, as well as the crystal chemistry doping process, are extensively analysed. X-ray diffraction measurements and Raman spectroscopy have been used to confirm that pure and Hf-doped BZO materials present a cubic structure. Extended X-ray absorption fine structure (EXAFS) indicate that Hf 4+ ions has replaced the Zr 4+ ions on the 6-fold coordination and a subsequent change on the Ba 2+ 12-fold coordination can be sensed. X-ray absorption near-edge spectroscopy (XANES) measurements reveal a local symmetry breaking process, associated to overlap of the 4d -2p and 5d -2p orbitals of Zr-O and Hf-O bonds, respectively. Field emission gun (FE-SEM) and high resolution transmission electron microscope (HRTEM) show the mesocrystalline nature of self-assembled BZHO nanoparticles under dodecahedron shape. In addition were performed first principle calculations to complement experimental data. The analysis of the band structures and density of states of undoped BZO and doped BZHO host lattice allow a deep insight on the main electronic features. The theoretical results help us to find a correlation between simulated and experimental Raman modes and allow a more substantial interpretation of crystal structure.

Optical and structural investigation of ZnO@ZnS core–shell nanostructures

“…The possible reason could be due to electronic and structural defects arising during the MAS synthesis. This same behaviour was already observed for other compounds in a previous work using the same synthesis methodology [28]. This band gap reduction can improve the light absorption of ZnO at visible range, favouring solar-cells applications.…”

“…The main advantages of solvothermal synthesis are related to homogeneous nucleation processes, ascribed to elimination of the calcinations step to produce very low grain sizes and high purity powders [27]. Besides the association of microwave radiation to solvothermal method generates a physical-chemical hydride synthesis methodology [28].…”

A DFT investigation of the role of oxygen vacancies on the structural, electronic and magnetic properties of ATiO3 (A = Mn, Fe, Ni) multiferroic materials

“…This method is helpful to clarify the nature of electron-hole localization in the constituent clusters inside the crystalline structure, providing an atomic level point of view of the fundamental mechanism associated with electron excitation and localization which are responsible for many phenomena, such as photoluminescence and photocatalysis. [63][64][65][66] In this formalism, the charge accumulation mechanism could be described as follows using the neutral…”

Mechanism of photoluminescence in intrinsically disordered CaZrO3 crystals: First principles modeling of the excited electronic states

“…However, modeling the structure of excited electronic states and their properties using the firstprinciples electronic structure methods is still a huge challenge. To overcome this difficulty, numerous efforts by our research group have been made to understand the mechanism of PL emissions in SrTiO3, SrTiO3:Sm, CaWO4, BaZrO3, and BaZr1-xHfxO3 solid solutions based on the characterization of excited electronic states [31][32][33][34][35][36][37] respectively, as the constituent building blocks of this material [49]. There are several reports on the electronic structure calculations performed to study CZO in the ground state [50][51][52][53][54][55].…”