Dielectric loss tangent of sapphire single crystal produced by edge-defined film-fed growth method

Abstract

We investigated the dielectric loss tangent (tan δ) of sapphire single crystals produced by edge-defined film-fed growth (EFG) method using a dielectric resonator with YBa 2Cu 3O y (YBCO) films. Surface resistance ( R s) of the YBCO film was low enough to obtain high resolution of tan δ measurement. For comparison, tan δ of the sapphire prepared by the Czochralsky (Cz) method was also evaluated. Measurements of 14 sapphire rods showed that EFG sapphire tends to have lower tan δ than Cz sapphire, while defects in Cz crystal were 1/14–1/2 less than that in EFG crystal. It means that the number of defects does not influence tan δ, if the density of defects is within the order of 10 4/cm 2. In most EFG sapphire the value of tan δ at 30 K was estimated to be <1.0×10 −7. It is usable for R s measurement of high critical temperature superconducting materials.