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The electrical conductivity σ and the thermal conductivity λ were investigated at varying temperature (40 < T < 120°C) for two sulphate compounds, anhydrous mercury(II) sulphate HgSO4 and cerous(III) sulphate Ce2(SO4)3 • H2O. It seems likely that each of the two sulphate salts undergoes structural phase transition around 90°C. The differential thermal analysis thermogram was carried out as an aid for confirming of the observed phase transitions. The mechanism of the heat transfer is mainly due to phonons. Interpretation of the obtained data was given on the basis of the reorientational motion of the SO4--ions.

A series of samples of the type Ni0.65Zno.35CuxFe2-xO4 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by means of a ceramic technique. The existence of a single phase was confirmed in X-ray studies. The dielectric constant K and dielectric loss D were measured at different temperatures at a frequency of 1 kHz. The pronounced increase in the dielectric constant at the transition temperature is due to the phase transformation from the ferrimagnetic to the paramagnetic state. The decrease in the dielectric loss with temperature is due to the reduction in the relaxation time of the hopping electrons and holes. The Tawfik constant was calculated in the ferrimagnetic state and was found to be correlated to the dielectric constant.The polycrystalline ferrites are good dielectric materials. The dielectric properties of ferrites depend on many factors, including the sintering temperature and the preparation conditions. Ferrites have low conductivity, which is one of the reasons for their microwave applications.Many investigators have studied the dielectric properties of Ni-Zn ferrites [1], Mn-Zn ferrites [2,3], Mn-Mg ferrites [4] and Li-Ni ferrites [5]. The measurements [4,5] were carried out at room temperature in the frequency range 102 to l0 s Hz. It was found that e, e and tan 6 decrease with increasing Ni content in Li-Ni ferrites [5]. The value of the measured dielectric constant e was found to be of the order of 105. These results were explained on the basis of the model published in [5]. The same value of the dielectric constant was found for Mn-Zn ferrites [6]. The reported value for the dielectric constant at 103 Hz was 17, while the a.c. conductivity was 10.2-10 -9 ~,-~-1. cm-1 for Coo.49Zno.51Fe204 [7].

A series of samples of the type 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by a ceramic technique. The existence of a single phase was confirmed by Xray studies. The thermal conductivity and specific heat were measured at 53~ The thermal conductivity had a minimum value at x = 0.3, due to the maximum porosity at this composition. The phonon frequency was estimated to have an optimum value at x = 0.3, due to the increase in phonon scattering.