乌青铜型BaNd2Ti4O12微波介质陶瓷的电导和介电损耗

摘要

用固相反应合成了乌青铜型钛酸盐陶瓷BaNd2Ti4O12,并用电化学阻抗和微波介质谐振测试表征了不同热处理和钽掺杂对电导和微波介电损耗的影响.电导率随退火气氛(空气,氧气和氮气)的变化与缺陷反应平衡2Oxo—2V**o+O2↑+2e'和TixTie′←→Ti'Ti随氧分压的变化一致,表明BaNd2Ti4O12具有∏型导电性质.在空气和氧气中退火有利于减少包括Vxo,Ti'Ti和弱束缚电子在内的本征缺陷因而降低电导.而在低氧分压的氮气中进行退火处理,增加了缺陷的浓度,同时提高了电导率.在空气/氧气/氮气中的退火处理对微波介电损耗没有明显的影响,表明本征缺陷对微波介电损耗的影响可以忽略.空气退火处理样品的电导率和微波介电损耗低于空气淬火处理的样品:其中电导的变化与缺陷反应平衡相关,但空气退火降低微波介电损耗可能与退火消除晶格热应力有关.五价钽的掺杂降低了电导但增大了微波介电损耗.本研究表明空气退火处理能有效地改善BaNd2Ti4O12陶瓷的品质因子Q×f,其值提高了约12％.%Tungsten-bronze type titanate BaNd2Ti4O12 ceramics were synthesized by solid state reactions.The conductivity and microwave dielectric loss of the samples that were thermally treated under various conditions and Ta-doped were investigated by electrochemical impedance measurement and microwave dielectric resonator measurement.The variation in conductivity with annealing atmospheres of air,O2,and N2 was consistent with the defect equilibriums 2Oxo←→2V**o +O2↑+2e′ and Ti'Ti+e′←→Ti'Ti suggesting n-type conductance for BaNd2Ti4O12.Thermal treatment in air/O2 was found to favor the elimination of the native defects Vxo,Ti′Ti and weakly bound electrons thus decreasing the conductivity.Thermal treatment in a N2atmosphere,which had a low oxygen partial pressure,increased the defect content and the conductivity.Thermal treatment in air/O2/N2 did not clearly affect the microwave dielectric loss,suggesting that native defects have negligible effects on this property.The air-annealed sample was found to have lower conductivity and lower microwave loss compared with the air-quenched sample.The change in conductivity was found to be related to the equilibrium of the native defects but the change in microwave dielectric loss might be explained by the release of thermally induced lattice strain.Ta doping reduced the conductivity but increased the microwave dielectric loss.This work shows that air-annealing may be an efficient way to improve the Q×ffactor for BaNd2Ti4O12 ceramics,which was enhanced by ～12％.