BiFeO_(3)–BaTiO_(3)(BF–BT)based piezoelectric ceramics are a kind of high-temperature lead-free piezoelectric ceramics with great development prospects due to their high Curie temperature(TC)and excellent electrical...BiFeO_(3)–BaTiO_(3)(BF–BT)based piezoelectric ceramics are a kind of high-temperature lead-free piezoelectric ceramics with great development prospects due to their high Curie temperature(TC)and excellent electrical properties.However,large leakage current limits their performance improvement and practical applications.In this work,direct current(DC)test,alternating current(AC)impedance,and Hall tests were used to investigate conduction mechanisms of 0.75BiFeO_(3)–0.25BaTiO_(3)ceramics over a wide temperature range.In the range of room temperature(RT)−150℃,ohmic conduction plays a predominant effect,and the main carriers are p-type holes with the activation energy(Ea)of 0.51 eV.When T>200℃,the Ea value calculated from the AC impedance and Hall data is 1.03 eV with oxygen vacancies as a cause of high conductivity.The diffusion behavior of thermally activated oxygen vacancies is affected by crystal symmetry,oxygen vacancy concentration,and distribution,dominating internal conduction mechanism.Deciphering the conduction mechanisms over the three temperature ranges would pave the way for further improving the insulation and electrical properties of BiFeO_(3)–BaTiO_(3)ceramics.展开更多
无污染、低成本和高性能Cu_(1.8)S基类液态热电材料受到关注.但是,其过高的本征Cu空位和Cu离子迁移特性限制了其性能和电稳定性的进一步提升.本研究采用机械合金化结合放电等离子体烧结制备了一系列Cu_(1.8)S和Mn_(x)Cu_(1.8)S_(0.5)Se_...无污染、低成本和高性能Cu_(1.8)S基类液态热电材料受到关注.但是,其过高的本征Cu空位和Cu离子迁移特性限制了其性能和电稳定性的进一步提升.本研究采用机械合金化结合放电等离子体烧结制备了一系列Cu_(1.8)S和Mn_(x)Cu_(1.8)S_(0.5)Se_(0.5)(0.01≤x≤0.06)块体热电材料.随着Se和Mn的引入,体系由低熵Cu_(1.8)S(0.4R^(*))转变为中熵MnxCu_(1.8)S_(0.5)Se_(0.5)(1.2R^(*)).构型熵的增加不仅提高了体系的结构对称性,MnxCu_(1.8)S_(0.5)Se_(0.5)室温下呈立方相结构,还增大了Mn的固溶度.高浓度Mn固溶有效填补了过高的本征Cu空位,降低了载流子浓度,优化了能带结构,提升了电输运性能.熵工程一方面增大了Cu离子迁移势垒,抑制Cu离子迁移.750 K下,即使电流密度达到24 A cm^(-2),Mn_(0.03)Cu_(1.8)S_(0.5)Se_(0.5)的电阻也几乎没有变化,显示出优异的电稳定性;同时可降低声速,软化晶格,降低晶格热导率.Mn_(0.06)Cu_(1.8)S_(0.5)Se_(0.5)的块体样品在773 K时获得最大ZT值0.79,相较于初始样品提高了两倍.结果表明熵工程结合Cu空位工程是提升Cu_(1.8)S基热电材料性能的有效策略.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52072028,52032007)National Key R&D Program of China(No.2022YFB3807400).
文摘BiFeO_(3)–BaTiO_(3)(BF–BT)based piezoelectric ceramics are a kind of high-temperature lead-free piezoelectric ceramics with great development prospects due to their high Curie temperature(TC)and excellent electrical properties.However,large leakage current limits their performance improvement and practical applications.In this work,direct current(DC)test,alternating current(AC)impedance,and Hall tests were used to investigate conduction mechanisms of 0.75BiFeO_(3)–0.25BaTiO_(3)ceramics over a wide temperature range.In the range of room temperature(RT)−150℃,ohmic conduction plays a predominant effect,and the main carriers are p-type holes with the activation energy(Ea)of 0.51 eV.When T>200℃,the Ea value calculated from the AC impedance and Hall data is 1.03 eV with oxygen vacancies as a cause of high conductivity.The diffusion behavior of thermally activated oxygen vacancies is affected by crystal symmetry,oxygen vacancy concentration,and distribution,dominating internal conduction mechanism.Deciphering the conduction mechanisms over the three temperature ranges would pave the way for further improving the insulation and electrical properties of BiFeO_(3)–BaTiO_(3)ceramics.
基金supported by the National Key R&D Program of China(2018YFB0703603)the State Key Laboratory of New Ceramic and Fine Processing Tsinghua University(KF202111)。
文摘无污染、低成本和高性能Cu_(1.8)S基类液态热电材料受到关注.但是,其过高的本征Cu空位和Cu离子迁移特性限制了其性能和电稳定性的进一步提升.本研究采用机械合金化结合放电等离子体烧结制备了一系列Cu_(1.8)S和Mn_(x)Cu_(1.8)S_(0.5)Se_(0.5)(0.01≤x≤0.06)块体热电材料.随着Se和Mn的引入,体系由低熵Cu_(1.8)S(0.4R^(*))转变为中熵MnxCu_(1.8)S_(0.5)Se_(0.5)(1.2R^(*)).构型熵的增加不仅提高了体系的结构对称性,MnxCu_(1.8)S_(0.5)Se_(0.5)室温下呈立方相结构,还增大了Mn的固溶度.高浓度Mn固溶有效填补了过高的本征Cu空位,降低了载流子浓度,优化了能带结构,提升了电输运性能.熵工程一方面增大了Cu离子迁移势垒,抑制Cu离子迁移.750 K下,即使电流密度达到24 A cm^(-2),Mn_(0.03)Cu_(1.8)S_(0.5)Se_(0.5)的电阻也几乎没有变化,显示出优异的电稳定性;同时可降低声速,软化晶格,降低晶格热导率.Mn_(0.06)Cu_(1.8)S_(0.5)Se_(0.5)的块体样品在773 K时获得最大ZT值0.79,相较于初始样品提高了两倍.结果表明熵工程结合Cu空位工程是提升Cu_(1.8)S基热电材料性能的有效策略.
