Temperature Dependence Of Dielectric Permittivity Research Articles

Microwave dielectric behavior of PVDF and VDF-TrFE copolymer

Measurements of the temperature dependent microwave dielectric permittivity of PVDF and 60%–40% VDF-TrFE copolymer are presented. A cavity perturbation method is used. At room temperature a surprisingly high absorption of microwave power is observed, which decreases with decreasing temperature. This behavior seems to be connected with the ferroelectric-to-para-electric phase transition. With the copolymers a dependence of the complex permittivity on annealing temperature is found. A model considering paraelectric fluctuations is proposed.

Finite element modeling of the RF heating process

The heating of heterogeneous materials by radio frequency excitation is modeled by sequential electromagnetic and thermal analysis using the finite-element method. The electromagnetic analysis comprises electrostatic modeling using temperature-dependent complex dielectric permittivity to account for the energy dissipating losses in the material. The thermal analysis consists of a transient finite-element procedure with temperature-dependent thermal and material properties. The results show good agreement with transient thermal measurements. >

Physical properties of BaCo 2(PO 4) 2 in the high temperature region

The following paper presents the study on temperature dependence of dielectric permittivity, specific resistance, and magnetic susceptibility of the crystal phase of BaCo 2(PO 4) 2 which is stable at room temperature. The investigation within the temperature range 290–1000 K has indicated that the examined compound sustained four phase transitions during heating. Recording of the diffuse reflectance spectrum at room tempearture, made it possible to establish the fact that when in the corresponding phase, the Co 2+ ion exists in octahedral surroundings.

Structural phase transitions in Co(ClO 4) 2.6H 2O in temperature range 100–375 K

Investigation of Co(ClO 4) 2.6H 2O was carried out in a temperature range 100 – 375 K by the method of X-ray diffraction analysis (determination of unit cell parameters) and determination of temperature dependence of dielectric permittivity and magnetic susceptibility. The aim of the research was to investigate the existence of structural phase transitions, on which the existing data are contraversial. It was established that phase transitions occur at 344 K, 295 K, 243 K, 182 K, 155 K, 136 K and 122 K. Phase transitions at 295 K, 182 K, 136 K and 122 K have not yet been described in literature.

Dielectric properties and diffusion of ferroelectric phase transition in lead indium niobate

Abstract Temperature dependences of dielectric permittivity and tanδ in PbIn0.5Nb0.5O3 crystals where the degree of compositional order was changed by annealing at 400–1050 °C and subsequent cooling at different rates are determined. In these crystals the diffuse phase transition from paraelectric to ferroelectric phase is accompanied by the tanδ increase. In the vinicity of the transition between para- and antiferroelectric phases there exist no tanδ anomalies. Such anomalies may serve as a criterion allowing to distinguish ferro- and antiferroelectric transitions. The degree of ferroelectric transition diffusion depends on the cooling rate after annealing: the lower the rate, the higher the diffusion.

Structural phase transitions in Ni(ClO4)2.6H2O in temperature range 100–375 K

Abstract Investigation of Co(ClO 4 ) 2 .6H 2 O was carried out in a temperature range 100 – 375 K by the method of X-ray diffraction analysis (determination of unit cell parameters) and determination of temperature dependence of dielectric permittivity and magnetic susceptibility. The aim of the research was to investigate the existence of structural phase transitions, on which the existing data are contraversial. It was established that phase transitions occur at 344 K, 295 K, 243 K, 182 K, 155 K, 136 K and 122 K. Phase transitions at 295 K, 182 K, 136 K and 122 K have not yet been described in literature.

The dielectric permittivity dependences on the temperature and frequencies in diffuse phase transition ferroelectric lead magnesium niobate crystal

Abstract The temperature dependence of dielectric permittivity ϵ* after quenching from the temperatures within the range T=620 ÷ 1470 K to the room temperature and the low-frequency dielectric dispersion at the measuring frequencies v=10–1 ÷ 104 Hz have been studied in the diffuse phase transition ferroelectric PbMg1/3 Nb2/3O3. The anomalies of ϵ* (T) have been observed at T ˜ 650 K and T ˜ 770 K and after quenching at T ≃ 287 K. Three dispersion regions were found. The stages of the diffuse phase transition have been discussed using the data on the dispersion parameters.

Dependence of electric properties of Pb(ZrxTi1-x)O3 solid solutions on their composition

Temperature dependence of dielectric permittivity, electric conductivity and Seebeck coefficient in the vicinity of phase changes was studied for various Pb(ZrxTi1-x)O3 solid solution compositions.The dependence of electric parameters, ε, σ and α on proportional compositions of Pb(ZrxTi1-x)O3 was observed. Large changes in the measured parameters were found for compositions close to the morphotropic boundary, X ≈ 0.53, where great deviations of piezoelectric properties occur.

Dielectric mossbauer and magnetic investigations of ferroelectric-magnetics Sr6Nb9FeO30and Ba6Nb9FeO30

Abstract From the temperature dependences of dielectric permittivity the Curie temperatures of ferroelectric-magnetics with the potassium tungsten bronze type structure Sr6Nb9FeO30 and Ba6Nb9FeO30 were determined. It was shown that the magnetic ordering in these crystals may have antiferromagnetic character. The quadrupole splitting of the Mossbauer absorption spectrum of Sr6Nb9FeO30 also exists above the Curie temperature and is probably due to the distribution of the Nb5+ and Fe3+ ions.