DIELECTRIC DISPERSION OF TGS

Abstract

The ferroelectric dispersion of TGS is of Debye type with a single relaxation time ; only in a small temperature region around To we found a slight deviation, which may be caused by imperfections or inhomogenities. The quotient of the Curie constants in the microwave region was measured to 4.75, which is somewhat larger than the theoretic value predicted by thermodynamic theory. The activation energy is in the ferroelectric region 0.35 eV, whereas in the paraelectric region it is 0.02 eV or less, thus indicating that TGS doesn't undergo an order-disorder transition. In 1962 Hill and Ichiki [I] published their results on the ferroelectric dispersion of TGS. They measured a very large distribution of relaxation times in the whole temperature range. The real part of the dielectric constant, ' , showed a maximum at the Curie point in the whole microwave region. Also the early dispersion measurements on RS [2] gave a broad distribution, but now new measurements [3], [4] proofed, that RS shows a dispersion of Debye-type. We studied the ferroelectric dispersion of TGS, but we could not confirm Hill and Ichiki's results [ 5 ] , [6]. For frequencies up to 10'' cps we used a coaxial system. Particular care was taken for temperature homogenity, therefore we constructed a special sample holder, where the shorting piston is made of two concentric rings. The outer ring is movable and can be set over the sample until to the inner conductor. Thus a temperature difference between the two faces of the sample is compensated before measuring [6]. The admittance of the sample is received by a reflectometer set up. Experimental results. 1) Outside of a small region about the transition point the ferroelectric dispersion of TGS is well described by the Debye formalism with a single relaxation time : The E', E plots are circles with the center on the real axis. The frequency distribution on the circles is also conform with the Debye-type dispersion. If the relaxation frequency f, is eliminated from the Debye equations and drawn against the measuring frequency v, it is confirmed that the so receivedf, depends not on v. 2) Approaching the transition point the type of dispersion gradually changes to a slight distribution. In a very small temperature region from around 0.1 deg around To this distribution becomes much more pronounced. The development of the distribution angle a is seen from figure 1. The sharp peak at To