PHYSICAL PROPERTIES OF UO$sub 2$ SINGLE CRYSTALS. Quarterly Report No. 4, July 1-September 30, 1962

Technical Report · Thu Oct 31 04:00:00 EST 1963

OSTI ID:4731451

A new furnace for the preparation of larger crystals of UO/sub 2/ and for the study of various properties of refractory uranium compounds has been developed. After-heating at the end of the runs avoids quenching and thermal stressing of the deposits. An investigation on the controiled oxidation of single crystals of UO/sub 2/ by hydrogen-water vapor and argon-water mixtures has been started. The apparatus for the low-temperature measurements has been finished completely so that the experiments could be started. Depending on the heating power used, values varying between 0.15 and 0.19 at 208 deg K, 0.08 and 0.08 at liquid nitrogen temperature and 0.20 watt cm/sup -1/ deg k/sup -1/ at liquid helium temperature were found. These values are higher than those obtained on polycrystalline material. Electrical conductivity measurements between liquid nitrogen temperature and 800 deg K have been continued on samples with composition in the range UO/sub 2.0000/ - UO/sub 2.007/. The activation energies calculated from the log sigma vs. (1/T) curves varied between 0.34 and 0.19 ev depending on the O/U atomic ratio. It was found that the activation energy first decreases as the oxygen content decreases and then levels off in the neighborhood of 0.1% excess oxygen. For the single crystals of UO/sub 2/, Hall effect measurements by dc and ac techiques have yielded no measurable response. This indicates that the Hall mobility has to be smaller than 0.04 cm/sup 2//v sec at room temperature. The construction of an apparatus for the measurement of the thermoelectric power in the low temperature range has been nearly finished. Preliminary measurements showed a rather constant value of the thermoelectric power between 170 deg K and 520 deg K. The crystal remained p-type in the whole temperature range. Further evidence for the electrical conduction mechaniam in UO/sub 2/ by small polarons is discussed. The value of the coupling constant alpha for the lattice-hole interaction, the low mobility leading to high effective masses of the polaron, and the expected jump probability of a hole in UO/sub 2/ are arguments in favor of the polaron formation. A qualitative interpretation of the conductivity curves at low temperatures is given using Holstein's theory for small polaron diffusivity. The stady of anomalous absorption of electrons in UO/sub 2/ and of dislocation has been pursued further. First results of a complementary investigation to UO/sub 2/ in another non- metallic structure, wurtzite (lattice defects in wurtzite ZnS) were submitted for publication. (auth)

• Research Organization: Mol, Belgium. Centre d'Etude de l'Energie Nucleaire
• NSA Number: NSA-17-008804
• OSTI ID: 4731451
• Report Number(s): EURAEC-463
• Country of Publication: United States
• Language: English

Related Subjects

ABSORPTION
ARGON
DEFECTS
DIFFUSION
DISLOCATIONS
ELECTRIC CONDUCTIVITY
ELECTRONS
EXCITATION
FURNACES
HALL EFFECT
HEAT TREATMENTS
HYDROGEN
LATTICES
LOW TEMPERATURE
MEASURED VALUES
METALS, CERAMICS, AND OTHER MATERIALS
MONOCRYSTALS
OXIDATION
PHONONS
POLARONS
PREPARATION
QUENCHING
REPORT
THERMAL STRESSES
URANIUM DIOXIDE
WATER