Research on High-Specific-Heat Dielectrics.

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.

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Document Details

Document Type
Technical Report
Publication Date
May 11, 1987
Accession Number
ADA187248

Entities

People

  • B. R. Patton
  • C. F. Clark
  • N. S. Dalal
  • P. K. Kahol
  • W. N. Lawless

Tags

Communities of Interest

  • Advanced Electronics

DTIC Thesaurus Topics

  • Body Weight
  • Ceramic Materials
  • Composite Materials
  • Conductivity
  • Crystal Lattice Vibrations
  • Crystal Structure
  • Dielectric Permittivity
  • Dielectrics
  • Diffraction
  • High Temperature
  • Magnetic Fields
  • Magnetic Properties
  • Materials
  • Measurement
  • Phase Transformations
  • Specific Heat
  • Thermal Conductivity

Readers

  • Materials Science and Engineering.
  • Superconducting Magnet Technology
  • Surface Engineering/Surface Coating Technology.