Preparation And Properties Of High Dielectric Constant Materials With Good Temperature Stability

With the rapid development of microelectronics technology, smaller and smaller featuresizes of devices with high dielectric constant and excellent dielectric temperature stability arerequired. Generally, the ferroelectric perovskites possess high-dielectric constant and arewidely used as capacitive compenents. However, the strong temperature dependence ofdielectric constant in these materials seriously limits the application in many cases.Furthermore, most of the ceramics used in capacitor are PbTiO₃-based materials now. Becauseof the volatile and toxic nature of PbO, and its high vapor pressure during the sinteringprocess, the use of PbTiO₃-based materials is restricted by law, and environmental and safetyconcerns regarding proper handling, disposal and recycling of lead containing materials haverisen. So there is a compulsion to develop lead-free materials with high-dielectric constantand excellent dielectric temperature stability.Usually, the dielectric temperature stability of ferroelectric materials can be modified bydoping other chemical elements. Compared with the normal ferroelectrics, the dispersion ofthe dielectric peak in relaxor ferroelectrics is more obvious. Thus, the relaxor ferroelectricspossess good dielectric temperature stability. In addition, by integrating two or more materialswith complementary properties, new composite materials could offer high dielectric constantand good dielectric temperature stability. On the other hand, it’s also very important toexplore the dielectric relaxation mechanism in these high dielectric constant materials. In thiswork,(K_0.5Na_0.5)NbO₃-Sr₂NaNb₅O₁₅（KNN-SNN）,(K_0.5Na_0.5)NbO₃-Ba₂NaNb₅O₁₅（KNN-BNN）,(K_0.5Na_0.5)NbO₃-Sr_0.53Ba_0.47Nb₂O₆（KNN-SBN） and BaTiO₃-Bi(Zn_1/2Zr_1/2)O₃（BT-BZZ） systems were prepared by solid-state reaction method.Dielectric measurements revealed that all of KNN-SNN, KNN-BNN and BT-BZZsystems transformed from normal ferroelectric to relaxor ferroelectric with increasing thecontent of doping. And all of the three systems possessed high dielectric constant, lowdielectric loss and good dielectric temperature stability in a certain temperature range. Whenx=0.1, the KNN-SNN samples possess high dielectric constant （>1200）, low dielectric loss（<4%） and the temperature variation of capacitance （Δε/ε37℃） was within15%in thetemperature range of37-180℃. When x=0.075, the KNN-BNN samples with high dielectricconstant （1000-1500）, low dielectric loss （<3%） and small temperature variation ofcapacitance （Δε/ε200℃≤15%） were obtained in the temperature range from200to450℃. Forx=0.07, the BT-BZZ samples possess high dielectric constant （>2000）, low dielectric loss （≤4%） and small temperature variation of capacitance （Δε/ε27℃≤15%） in the temperature rangeof27-200℃; for x=0.1, the BT-BZZ samples possess high dielectric constant （>1000）, lowdielectric loss （≤5%） and small temperature variation of capacitance （Δε/ε100℃≤15%） in thetemperature range of100-300℃. In addition, the piezoelectric properties of KNN-SBNsystem were improved by doping SBN.