Gerald R. Miller

Electrical and mechanical relaxation in CaF2 doped with NaF

Abstract A loss peak caused by addition of NaF to CaF2 was studied by dielectric loss and internal friction methods. The observed relaxation times of the sodium ion-fluorine vacancy dipole in electrical and mechanical fields are given by equations (1) and (2). T elec. = 7.25 × 10 −15 exp 0·53 kT (1) Tx mech. = 3.29 × 10 −15 exp 0·53 kT (2) It is proposed that the dipole relaxation occurs by fluorine vacancy jumps in the 〈100〉 direction of the first coordination shell of the sodium impurity. A possible explanation of the observed peak broadening as a function of dipole concentration is offered.

High temperature steady-state creep of polycrystalline rutile, pure and doped with tantalum

The steady state creep of polycrystalline (5–60 μm) rutile, which is doped with 1 cation % tantalum, is controlled by a Nabarro-Herring lattice diffusion process at 1100 to 1200° C. Doping with tantalum significantly depresses the steady state creep rate by lowering the concentrations of titanium interstitials and oxygen vacancies. The concentrations of these defects, and hence the steady state creep rate of doped rutile, can be increased by decreasing the oxygen partial pressure below 10−7 to 10−8 atm at 1200° C. Tentative evidence is presented in support of the hypothesis that the steady state creep of polycrystalline, undoped rutile at 950 to 1100° C is controlled by interfacial defect creation and/or annihilation at grain boundaries. Interfacial controlled deformation rates are probably due to the large concentrations (and perhaps high mobilities) of cation and anion lattice defects which are present in pure rutile equilibrated in both oxidizing and reducing atmospheres. The steady state creep rate was a very weak inverse function of the grain size and essentially independent of the oxygen partial pressure.

The effects of dopant addition on sintering, electrical conductivity,fracture strength,and corrosion resistance of polycrystalline CaTiO3

The effects of dopant addition on sintering, electrical conductivity, fracture strength, and corrosion resistance of polycrystalline calcium titanate have been investigated for a wide list of potential substitutional dopants. Significant improvements of electrical conductivity at room temperature and corrosion resistance in molten KOH at 450° C have been observed in the polycrystalline calcium titanate specimens doped with tantalum and niobium and cerium and chromium, respectively. These results are in comparison to pure, reduced material. On the other hand, no appreciable effect of dopant addition has been observed on sinterability and fracture strength of the polycrystalline calcium titanate.