Low-Temperature Thermal Properties of Lithium Fluoride Containing Dislocations
Thermal conductivity κ and thermal diffusivity D = κ/pρ, where ρ is the density and C is the specific heat of the material, of Harshaw LiF crystals have been measured in the temperature range of 1.5 – 15 K by the temperature-wave method developed by the present authors.1 Specimens with the (100) faces and 0.2 × 0.3 × 6 cm in size were annealed at 750° C for 2.5 hr in argon atmosphere and then side faces were roughened with fine emery. Crystal dislocations were introduced in the specimen by compression along its axis by a loading machine. At that time, sides of the specimen were supported by brass blocks to prevent buckling, and the ends were covered with indium sheets. The amount of the deformation was 0.42 – 10.3% in reduction of length. Then we shaped a carbon-film heater (H) and two thermometers (T1, T2) around the sides of the specimen by painting thin layer of Aquadag, and H, T1, and T2 were distant from an end of the specimen by about 0.3, 0.8, and 1.8 cm. The other end of the specimen was lapped with soft thin copper foil and covered with Apiezon N grease and mounted to a copper block attached to the bottom of a small chamber in a cryostat. The chamber filled with liquid helium acted as a heat sink. Temperature of the specimen was controlled by pumping the liquid helium and by adjusting the current in a heater wound around the heat sink.
KeywordsThermal Diffusivity Heat Sink Liquid Helium Copper Block Lithium Fluoride
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