| ABO3-type Perovskite material is a series of ceramic oxides with rich physical properties.Because ABO3-type Perovskite materiasls behave perfect dielectric,piezoelectric and ferroelectric propertie.When some dopant were introduced into ABO3-type Perovskite structures,leading to crystal defect,usually,materials could exhibit better performance.This paper is to research and discuss the dielectric properties of several ABO3-type Perovskite ceramic materials(SrTiO3,BaZrO3,KTaO3)as the subjects investigated.The research results are as follows:(1)SrTi1-x(Al,Nb)xO3(x=0,0.005,0.05,and 0.1)ceramic samples were prepared using the conventional solid-state reaction method.The dielectric properties of these samples were investigated in temperature range of 320-870 K and frequency range of 102-106 Hz.The samples showed two dielectric relaxations related to grain and grain boundary.The effects of(Al,Nb)co-doping were found to have influence on the grain-boundary relaxation by reducing its activation energy and enhancing the conductivity.Our results showed that it is unsuitable to enhance the dielectric properties of SrTiO3 via(Al,Nb)co-doping.(2)BaZrO3(BZO)powders were synthesized by solution combustion based on the glycine nitrate process.Sintering conditions of BZO sample was optimized by varying the sintering temperature and dwell time.Dielectric properties of the sintered samples were investigated in the temperature range of 300-1080 K and frequency range of 102-106 Hz.The sample sintered at 1973 K for 12 h was found to show the best dielectric properties.Detailed investigations on this sample revealed an incipient ferroelectric behavior in the temperature range below 420 K and a colossal dielectric behavior above 420 K.The colossal dielectric behavior was composed of two thermally activated relaxations.The low-temperature relaxation being was argued to be a dipolar relaxation caused by oxygen vacancies hopping motion inside grains and the high-temperature one was ascribed to be a Maxwell-Wagner relaxation due to the oxygen vacancies being blocked by the sample/electrode contacts.(3)Ceramic samples of BaZr0.8Y0.2O3-δ(BZY)were synthesized by solution combustion method based on the glycine nitrate process.The dielectric properties were investigated in the temperature range of 300-870 K and frequency range of 102-106 Hz.Two types of carriers,hydroxyl ions and oxygen vacancies,coexisted in the material and led to three sets of relaxations.The activation energies were calculated to be 0.50,0.65,and 1.27 eV for low-,middle-and high-temperature relaxations,respectively.The low-temperature relaxation was ascribed to be a dipolar relaxation resulting from the OHO·-Y dipole.The middle-and high-temperature relaxations were argued to be Max well-Wagner relaxations associated with space charges caused by hopping oxygen vacancies blocked by grain boundaries and sample-electrode contacts,respectively.(4)KTaO3 ceramic samples were prepared via conventional solid state reaction route.The dielectric properties of KTaO3 were investigated in the temperature from room temperature to 1000 K and the frequency range of 102-106 Hz.The sample exhibited an abnormal dielectric behavior contrary to the traditional thermally activated behavior in the temperature range below 450 K.Our results revealed that the sample was very sensitive to humidity,leading to a metal-insulator transition(MIT)at 473 K.It was the the positive temperature coefficient of resistance the MIT that results in the abnormal dielectric behavior.When temperature was higher than 500 K,the sample showed two normal dielectric relaxations following thermally activated behavior.The low-and high-temperature relaxations were argued,respectively,to be related to dipolar relaxation and Maxwell-Wagner relaxations due to oxygen vacancies hopping inside grains and then being blocked by grain boundaries. |
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