Reduction Of Low-frequency Dielectric Loss In CaCu₃Ti₄O₁₂ And (In_0.5Nb_0.5)_xTi_1-xO₂ Ceramics

Dielectric materials are fundamental materials for electronic products such as communications,automobiles and household appliances,which are used to make capacitive devices because of their dielectric properties.Thus,dielectric materials are widely used in capacitors,filters,resonators and dynamic memories.In recent years,with the rapid development of household appliances technology,medical technology and navigation technology,the demand for electronic devices and products has become higher and higher,which makes electron component develop towards miniaturization,large capacity and high quality.Thus,exploring the dielectric materials with high permittivity,low dielectric loss and stable performance is of great significance.In recent years,CaCu₃Ti₄O₁₂?CCTO?with perovskite structure and donor/acceptor co-doped-(In_0.5Nb_0.5)_xTi_1-xO₂?INTO?with rutile structure have attracted much attention because of unusually high permittivity,low dielectric loss,good frequency stability at room temperature and temperature stability.However,the low-frequency dielectric loss of CCTO and INTO ceramics is still relatively high,which fails to reach the requirement of practical application.Thus,the thesis is devoted to reducing the low-frequency dielectric losses of CCTO and INTO ceramics.In this thesis,CaCu₃Ti₄O₁₂2 ceramic samples are prepared by sol-gel method,and their structures,microstructures and dielectric properties are analyzed and studied.The high permittivity??>10⁴?is exhibited in CCTO ceramics.When sintered at 1080^oC,the dielectric property of CCTO ceramic sample is more excellent that of other samples.The permittivity is above 3×10⁴ at the frequency range of 20 Hz–200 kHz,and the dielectric loss is 0.028 at 1kHz.Besides,(In_0.5Nb_0.5)_xTi_1-x-x O₂?x=0.01,0.05 and 0.1?ceramic samples are prepared by solid-state method.The structures,microstructures and dielectric properties are analyzed and studied.The high permittivity??>10⁴?is exhibited in all INTO ceramics.When sintered at1350^oC,the dielectric property of INTO ceramic sample?x=0.05?is more excellent than that of other samples.The dielectric constant was above 1×10⁴at the frequency range of 20 Hz–1MHz,and the dielectric loss was less than 0.05 at 1 kHz.A series of NaCu3Ti3Sb0.5Ta0.5O12?NCTSTO?ceramics are prepared by the traditional solid-state reaction method.By investigating the complex impedance map of NCTSTO ceramics,it was found that it had insulating grain boundaries and semi-conducting grains.Moreover,a small amount of CuO secondary phase and Cu²⁺/Cu¹⁺,Ti⁴⁺/Ti³⁺,Sb⁵⁺/Sb³⁺and Ta⁵⁺/Ta³⁺aliovalences are found to exist in NaCu₃Ti₃Sb_0.5Ta_0.5O₁₂2 ceramics through characterization analysis.Internal barrier layer capacitance effect is suggested to be the origin of the high dielectric-permittivity properties in NaCu₃Ti₃Sb_0.5Ta_0.5O₁₂2 ceramics.Furthermore,CCTO/x(In_0.5Nb_0.5)_0.05Ti_0.95O₂?x=0,0.5,1 and 2?composite ceramic samples are prepared in this thesis.The structures,microstructures and dielectric properties are analyzed and studied.When sintered at 1040^oC,the permittivity and dielectric loss of composite ceramics decrease as the ratio of INTO increased.For composite ceramic of x=2,the permittivity is above 2000 and dielectric loss is less than 0.01 in the frequency range of100 Hz–10 kHz and the minimum dielectric loss value is 0.0073,as well as the permittivity maintains good frequency stability at room temperature and temperature stability of CCTO and INTO ceramics.At present,the many researchers agree that the high dielectric properties of INTO ceramics originate from an internal barrier layer capacitance?IBLC?effect.According to the IBLC mechanism,increasing the grain boundary insulation is an effective way to reduce the low-frequency dielectric loss of INTO ceramics.In order to increase grain boundary insulation,reduce leakage current,and reduce the low-frequency dielectric loss,we coated ZrO₂ with good insulation to outside of INTO grains.The INTO/xZrO₂?x=0,0.01,0.02,0.05and 0.1?composite ceramic samples are synthesized in this thesis.The structures,microstructures and dielectric properties are analyzed and studied.The high permittivity is observed in the INTO/ZrO₂ composite ceramics,while the dielectric loss is above 0.1,not reaching desired results.After annealing at 800^oC in air,the dielectric loss of INTO/ZrO₂composite ceramics decreases significantly.After annealing for the ceramic of x=0.05 sintered at 1400^oC,dielectric loss was below 0.05 at the frequency range of 100 Hz–50 kHz and the minimum value is 0.02 at 3 kHz.In order to find out the reason that the low-frequency dielectric loss decreases,we analyze the complex impedance spectroscopies of the ceramic samples before and after annealing,finding that the grain boundary resistance of the ceramic samples increases significantly after annealing while there is little change for the grain resistance.So we believe that the decrease of low-frequency dielectric loss for INTO/ZrO₂composite ceramics was mainly caused by grain boundary resistance increasing.