Accession Number : ADA187248

Title :   Research on High-Specific-Heat Dielectrics.

Descriptive Note : Final technical rept. 1 Apr 86-30 Apr 87,

Corporate Author : CERAMPHYSICS INC WESTERVILLE OH

Personal Author(s) : Lawless, W N ; Clark, C F ; Patton, B R ; Kahol, P K ; Dalal, N S

PDF Url : ADA187248

Report Date : 11 May 1987

Pagination or Media Count : 190

Abstract : This Annual Report details a program of research on composite spinel ceramic materials with enormous specific heat maxima in the temperature range 5-20 K. The results obtained so far have suggested an attractive picture for the ordering phenomena in the B-site spinels, CdCr2O4 and ZnCr2O4. Significant progress in characterizing and controlling the fabrication of the spinel materials has been made. Pure powders, compacted disks, as well as the 9/1 columbite composite have been made and characterized. Magnetocaloric experiments reveal no trace of hysteresis, which means that the phenomena involved in the low temperature transitions in the Zn and Cd spinels must involve second order transitions. Adiabatic demagnetization cooling above TN and also at low temperatures is indicative of paramagnetic spins, while a region of demagnetization heating just below TN seems to indicate anti-ferromagnetic ordering. Measurements have also discovered an amazing anomaly in the dielectric constant at the anti ferromagnetic transition. Keywords: Ceramic, Magnetocaloric, Spinels.

Descriptors :   *CERAMIC MATERIALS, *COMPOSITE MATERIALS, *DIELECTRIC PROPERTIES, *SPINEL, ADIABATIC CONDITIONS, CONSTANTS, COOLING, DEMAGNETIZATION, DISKS, HEATING, HYSTERESIS, LOW TEMPERATURE, MATERIALS, POWDERS, PURITY, SPECIFIC HEAT, TRANSITIONS

Subject Categories : Ceramics, Refractories and Glass

Distribution Statement : APPROVED FOR PUBLIC RELEASE