摘要:
利用传统固相反应法成功制备出Nb掺杂量x不同的Ca0.9Yb0.1Mn1-xNbxO3热电陶瓷.X射线衍射分析和扫描电子显微镜分析表明：样品均形成了单一的钙钛矿正交结构,空间群为Pnma.晶格常数a和晶胞体积随着Nb掺杂量x的增加而增大,陶瓷样品具有很好的结晶度和很高的致密性,相对密度达到97%左右.在300—1100K温区,测试得到了样品的电阻率和Seebeck系数,发现在低温区样品表现为半导行为,而在高温区表现为金属导电行为.随着Nb掺杂量x的增加,半导-金属导电行为的转变温度向高温区移动.电阻率随着掺杂量的增加而增大,仅在高温区x=0.03样品的电阻率略比未掺杂Nb样品的低.这是由于Nb的掺杂不仅引入载流子,同时还引起MnO6八面体的扭曲,造成载流子的局域化所致.在整个测试温区内,样品的Seebeck系数全为负值,表明电子是主要载流子.样品的Seebeck系数的绝对值随温度的升高近似呈线性增加,但是随Nb掺杂量x的增加依次减小.计算表明,未掺杂Nb的样品在温度为497K时最大功率因子达到297μW/K2m,并且在整个测试温区表现了良好的温度稳定性.
Abstract:
Different Nb doped Ca0.9Yb0.1Mn1-xNbxO3 ceramics are successfully synthesized by the conventional solid state reaction technique.The crystal structures are of orthorhombic phase,belonging to the Pnma space group.The lattice constant and the volume increase with the increase of Nb content.Relatively high density is around 97%.Scanning electron microscope （SEM） images show that samples are well crystallized.The electrical resistivity and the Seebeck coefficient are measured in a temperature range between 300 and 1100 K.At low temperatures,the electrical resistivity shows a semiconductive-like behavior.At high temperatures,the electrical resistivity exhibits a typical metallic conductive behavior.The semiconductor-metal transition temperature shifts toward a higher temperature with the increase of Nb content.The electrical resistivity increases with Nb dopant,except that the electrical resistivity for x=0.03 is slight lower than that fox x=0.00 sample at high temperature range.This conductivity behavior can be understood as the fact that though Nb doping can introduce more carriers,it also distorts the MnO6 octahedra,and causes the carrier localization.The values of Seebeck coefficient are all negative,indicative of an n-type electrical conduction.The absolute value of Seebeck coefficient increases with temperature increasing,but decreases with the increase of Nb content.The highest power factor is obtained to be 297 μW/K2m at 497 K in the x=0.00 sample,and the power factor of this sample is less independent of temperature in the whole measured temperature range.
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