City Research Online

Abstract

A study of vacancy lifetimes in platinum using modulation techniques is described. The theory of producing the sinusoidal temperature oscillations by two related methods and the application to vacancy lifetime measurements using an a.c. bridge technique is given.

An account is briefly given of an experiment measuring the third harmonic voltage generated across an a.c. heated wire sample. The sample was a platinum wire of 50mm diameter whose temperature was modulated at ~40Hz over a mean temperature range of 1400K-1800K. A modified form of de Sauty's Bridge was used to obtain these results. Results for the temperature coefficient of resistivity as a function of temperature were calculated. The agreement with accepted results for the temperature coefficient of resistivity was poor due to difficulties and inaccuracies associated with the use of the a.c. bridge when not implemented as a null detector.

A second experiment is described in which the a.c. bridge was used to determine the equivalent impedance of an a.c. heated platinum wire of 50mm diameter over the temperature range of 1400K - 1800K. The frequency of the heating current was in the range of ~40Hz ~~180Hz. The absolute values and temperature dependence of the temperature coefficient of resistivity calculated from the equivalent impedance results are in agreement with accepted results of other workers at low modulating frequencies (~ 40Hz), At higher modulating frequencies a reduction in the temperature coefficient of resistivity at temperatures >1650K was discerned. These results are discussed and compared with theory : they are interpreted as due to a vacancy lifetime of ~1ms at 1800K.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QC Physics
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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