PHYSICAL PROPERTIES OF UO$sub 2$ SINGLE CRYSTALS. Quarterly Report No. 5, October 1, and December 31, 1962
Several runs were made to prepare single crystals of UO/sub 2/ for studies at CEN and for satisfying requests from other institutions. The gyration method for spheroidization of single crystals was improved. An equipment for the sintering experiments and for observation of the necks formed between the particles was constructed. In a first experiment, no sintering couid be observed at temperatures below 1700 deg C. For the mass-spectrometric determination of the U/sub 235//U/sub 238/ ratio, a device was developed allowing the removal of parallel layers of a thickness of 0.1 mu . UO/sub 2/ single crystals (as grown, annealed, and irradiated) were studied by transmission electron microscopy. Observations of small dislocation loops, small angle boundaries, dislocations and fission tracks were made. The method developed for thinning UO/sub 2/ crystals was also applied to ferroelectric BaTiO/sub 3/. Some modifications were introduced to the apparatus for the low temperature measurements. A few determinations of the thermal conductivity at room temperature and at liquid nitrogen temperature were performed. The values obtained (0.210 watts cm/sup -1/ deg K/sup -1/ at 288 deg K and 0.061 at 77.8 deg K) confirm previous conclusions. The construction of the apparatus for high temperature measurements is still in progress. The Hall-effect measurements were extended to high-ohmic crystals. The absence of any Hall response indicates that the Hall mobility has to be smaller than 0.015 cm/sup 2/ V/sup -1/ sec/sup -1/ at room temperature. The thermoelectric power of three single crystals of UO/sub 2/ was measured between 170 deg K and 320 deg K with a slightiy modified apparatus. From the sign of the Seebeck coefflcient, it follows that the conduction in UO/sub 2/ is of p-type in the temperature region investigated. The curves show a rather constant value for the thermoelectric power as a function of thc temperature. The study of the effects of neutron irradiation on the electrical conductivity of UO/sub 2/ was started. Preliminary results show a marked increase in the resistivity, accompanied by a decrease in the activation energy. Puise annealing experiments in irradiated UO/sub 2/ indicate that practically no annealing occurs between room temperature and 300 deg C. Another transport mechanism, the tunneling mechanism'', which could eventually explain the electrical behavior of UO/sub 2/, was studied. It is shown that tunneling of the charge carriers cannot account for the effects observed in UO/sub 2/. This is a new argument in favor of the occurrence of small polarons in UO/sub 2/. (auth)
- Research Organization:
- Mol, Belgium. Centre d'Etude de l'Energie Nucleaire
- NSA Number:
- NSA-17-016642
- OSTI ID:
- 4724952
- Report Number(s):
- EURAEC-524; R-2204
- Country of Publication:
- United States
- Language:
- English
Similar Records
PHYSICAL PROPERTIES OF UO$sub 2$ SINGLE CRYSTALS. Quarterly Report No. 4, July 1-September 30, 1962
THERMAL CONDUCTIVITY OF UO$sub 2$
Related Subjects
CARRIERS
DEFECTS
DISLOCATIONS
ELECTRIC CHARGES
ELECTRIC CONDUCTIVITY
ELECTRON MICROSCOPY
ELECTRONS
FISSION PRODUCTS
HALL EFFECT
HIGH TEMPERATURE
IRRADIATION
LAYERS
LOW TEMPERATURE
MASS SPECTROMETERS
MATERIALS TESTING
METALS, CERAMICS, AND OTHER MATERIALS
MONOCRYSTALS
NEUTRON BEAMS
PARTICLE TRACKS
PHONONS
PLANNING
POLARONS
PREPARATION
PULSES
QUANTITATIVE ANALYSIS
ROTATION
SINTERING
SPHERES
THERMAL CONDUCTIVITY
THERMOELECTRICITY
THICKNESS
URANIUM 235
URANIUM 238
URANIUM DIOXIDE