Project Details
Anion-hydride-exchange as a tool for material design - substitution effects in fluorides, fluoride borates and fluoride phosphates studied by local probes
Applicant
Professorin Dr. Nathalie Kunkel
Subject Area
Solid State and Surface Chemistry, Material Synthesis
Term
from 2018 to 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 396943587
Partial substitution of anions by hydride for materials design is recently attracting a lot of attention and attempts to better localize small amounts of hydride anions in materials play an important role. It was shown that the substitution induces significant changes in materials properties, for example in the conductivity., meaning that incorporation of hydride significantly modifies the physical and chemical properties of a material. The nature of this effect is not yet completely understood, but a relation with the high polarizability of the hydride anion is assumed. Even though neutron and X-ray diffraction methods are a very powerful tool to describe hydrides, information beyond the averages structural data, such as local information regarding covalence and polarizability are essential in order to gain a deeper understanding, for example when materials are only partially substituted by hydride.Within the frame of this project we are proposing the use of local probes besides diffraction methods. In relation with sufficiently large band gaps, these represent a suited method, for example together with rare earth ion doping. Both 4f-4f and 5d-4f transitions can deliver information on the local environment. The latter are known for their sensitivity towards differences in polarizabilities, as the example of the redshift of the Eu2+ emission energies in nitrides compared to oxides or fluorides has shown. The orange or red emission usually found in nitrides is nowadays commercially used in solid state lighting applications. First preliminary works in pure hydrides strongly suggest that a similar effect is taking place in a hydridic environment.Here, we are aiming at exploring hydride substitution as a tool for materials design. As model systems for the incorporation of hydride by substituting fluoride anions, first we have chosen pure fluorides, then fluoride borates and fluoride phosphates. Beside structural characterization by means of X-ray and neutron diffraction methods, we will especially investigate how rare earth ions can serve as optical probe. These studies will be supplemented by the use of electron paramagnetic resonance spectroscopy and nuclear magnetic resonance spectroscopy. In summary, the project will contribute to the knowledge on the existence and the chemistry of hydride substituted compounds and also on the correlation between structural and spectroscopic properties.
DFG Programme
Research Grants