A sample holder for simultaneous neutron and dielectric spectroscopy – dielectric tests with glycerol, glycerol-water, water and phosphoric acid

Abstract

We report on dielectric test measurements of a rectangular flat sample holder which serves as capacitor and which is aimed for simultaneous neutron and dielectric (n-DE) spectroscopy of acidic liquid samples. We describe technical details of the sample holder assembly and the dielectric and neutron equipment as well as the sample preparation procedure of the air sensitive acidic samples. The sample holder was characterised off-line from the neutron spectrometer by dielectric spectroscopy, but using the standard IN16B cryofurnace with a dielectric sample stick with 4-wire connection and a Novocontrol equipment, previously setup by a collaborative effort between ILL and Roskilde University. Temperature-dependent dielectric scans on standard samples (glycerol, glycerol-water, and Milli-Q water) were measured in the frequency range between 0.27 Hz and 1 MHz. Step-like temperature changes allowed to probe the temperature equilibrium conditions and continuous temperature changes were made to mimic typical IN16B backscattering neutron fixed window scans. Both type of scans were carried out in cooling and in heating. The standard samples show that our dielectric setup with flat sample holder is well suited for simultaneous n-DE-experiments. On the other hand, the dielectric scan on phosphoric acid reveals the limitations of our setup in case of high sample conductivities, but also shows that the DC-conductivity can still be accessed in a sufficiently wide low temperature range where the onset of conductivity can be simultaneously probed with the change in proton dynamics as seen by neutron spectroscopy.