Ag^+,Sr^(2+),Yb^(3+)双掺杂对Ca_3Co_4O_(9-δ)热电性能的影响

Effects of Ag^+,Sr^(2+),Yb^(3+) Dual-doping on Thermoelectric Properties of Ca_3Co_4O_(9-δ)

采用溶胶-凝胶和冷压方法,在Ca3Co4O9-δ体系中引入不同量的Ag^+,Sr^(2+)或Yb^(3+)离子制备了可在300~870 K下稳定存在且热电性能优良的陶瓷材料Ca_(3-x-y)Ag_xSr_yCo_4O_(9-δ),Ca_(3-x-z)Ag_xYb_zCo_4O_(9-δ)和Ca_(3-y-z)Sr_yYb_zCo_4O_(9-δ)(x,y,z=0.1,0.15,0.2).通过X射线衍射(XRD)、傅里叶变换红外光谱(IR)和扫描电子显微镜(SEM)等手段对产物进行表征.结果显示,所制备的样品纯度较高,晶粒均匀,晶粒间较致密,适量的Ag^+,Sr^(2+),Yb^(3+)离子取代Ca^(2+)离子固溶到晶体中使制备的双掺杂材料晶胞体积发生了变化,但并未引起晶体对称结构的变化.电阻率和Seebeck系数结果表明,双掺杂优化了样品载流子的浓度,使样品电阻率不断减小,并使Seebeck系数的值不断增大.经过计算可知,Seebeck系数随电子有效质量的增大而增大.热导率结果表明,双掺杂的样品热导率随掺杂元素的不同而变化,计算结果显示声子热导依然在样品中占据主体贡献,这与Ca_3Co_4O_(9-δ)单掺杂Ag^+,Sr^(2+)或Yb^(3+)的结果吻合.随着温度的升高,双掺杂样品Ca_(2.7)Ag_(0.2)Yb_(0.1)Co_4O_(9-δ)在870 K下热电优值(ZT)值达到最大(0.18).

A series of ceramic materials,Ca3-x-y Agx Sry Co4 O9-δ,Ca3-x-z Agx Ybz Co4 O9-δ and Ca3-y-zSry YbzCo4O9-δ（x, y, z=0. 1, 0. 15, 0. 2）which worked from 300 K to 870 K with excellent thermoe-lectric properties, was prepared by sol-gel and cold-pressing method. The XRD, IR and SEM results reveal that the prepared samples are uniform crystal particles with high purity. Ag^＋ Sr^2＋ and Yb^3＋ ions have replaced the position of Ca2~ ions and they are dissolved in the crystal, which changes the cell volume of the dual-do- ping materials but does not change the crystal symmetric structure. The characterization results of resistivity and Seebeck coefficient reveal that the concentration of carrier is optimized by dual doping, accordingly the resistivity decreases continuously with the doped different materials and the value of Seebeck coefficient increa- ses continuously with the doped different materials. It can be concluded from the calculations that the electron effective mass contributes to the increase of Seebeck coefficient. The characterization results of thermal conduc- tivity indicate that the thermal conductivity of dual doped samples decreases with the increase of temperature, and the phonon thermal conductivity still contributes more in the prepared system, which is consistent with the results of Ag^＋,Sr^2＋,Yb^3＋ single doped Ca3Co4O9-δ samples. The figure of metrt ZT of Ca2. 7Ag0.2Yb0. 1 Co409-δ exceeds 0. 18 at 870 K.