Disputation: Øystein Slagtern Fjellvåg
M.Sc. Øystein Slagtern Fjellvåg at the Department of Chemistry is defending the thesis Oxyhydrides – Synthesis, Crystal Structure and Properties for the degree of Philosophiae Doctor.
Øystein Slagtern Fjellvåg
Trial lecture - time and Place
August 15th, 10:15 AM, Auditorium 2, Kjemibygningen
«Mixed anion materials»
Å nyttiggjøre og forbedre forståelsen av sammenhengen mellom syntese, atomarrangement og egenskaper for materialer som kan anvendes i moderne teknologi er et viktig forskningstema innen kjemi og materialvitenskap. I dette arbeidet er materialklassen oksidhydrider undersøkt. Studiet har gitt ny innsikt i syntesemetode, forståelse av forbindelsenes termiske stabilitet samt sammenheng mellom hvordan atomarrangement og kjemiske bindingsforhold påvirker ionisk ledningsevne.
Main research findings
This thesis focus on the research of the new and scarcely explored material class oxyhydrides, where the anionic lattice consists of both oxide and hydride anions. Selected oxyhydrides described by the formula La2‑xNdxLiHO3 (0 ≤ x ≤ 2) have been obtained by a halide salt flux method in large quantities (gram scale). We describe key factors for preparation of oxyhydrides by this approach, and we discover lithium chloride to serve as an excellent flux also below its melting temperature, opening for a completely new temperature range for synthesis of oxyhydrides. Phase pure Nd2LiHO3 was in this work produced phase pure for the first time. Neutron diffraction was employed to study the long range and local structure of La2LiHO3, and neutron spectroscopy combined with computational methods yields new insight the migration of hydride anions in the compound based on evaluation of the chemical bonding.
LaSr3Fe3O9 is found to be a new layered compound with a G-type antiferromagnetic structure which is immiscible with LaSr3Fe3O10‑δ. Preliminary neutron diffraction experiments on corresponding oxyhydrides prepared by topotactic anion-exchange with CaH2, indicate successful preparation of an oxyhydride with the composition LaSr3Fe3H1.1O8.9.