Ca掺杂对ZnO氧化物热学性能的影响

在密度泛函理论和线性响应的密度泛函微扰理论基础上的第一性原理计算的方法研究了Ca掺杂对纤锌矿结构氧化物ZnO热学参数和热学性能的影响。研究结果表明,Ca掺杂ZnO氧化物晶格a,b,c轴均有所增大;在计算温度区间,纯的ZnO和Ca掺杂的ZnO的晶格热容均随温度升高不断增大;Ca掺杂的ZnO具有较高的晶格热容;纯的ZnO和Ca掺杂的ZnO的晶格热容在最高温度900K分别达到16.5 Cal.mol-1K-1和31.7Cal.mol-1K-1。纯的ZnO和Ca掺杂的ZnO的德拜温度 均随温度升高不断增大,Ca掺杂的ZnO的德拜温度 均高于纯的ZnO。Ca掺杂在ZnO中引入了新的振动模式。Ca掺杂ZnO氧化物应该具有较高的晶格热导率。     

Synthesis, thermionic emission and magnetic properties of (NdxGd1-x)B6

Polycrystalline rare-earth hexaborides(NdxGd1-x)B6(x = 0,0.2,0.6,0.8,1) were prepared by the reactive spark plasma sintering(SPS) method using mixed powder of GdH2,NdH2 and B.The effects of Nd doping on the crystal structure,the grain orientation,the thermionic emission and the magnetic properties of the hexaboride were investigated by X-ray diffraction,electron backscattered diffraction and magnetic measurements.It is found that all the samples sintered by the SPS method exhibit high densities(> 95%) and high values of Vickers hardness(2319 kg/mm2).The values are much higher than those obtained in the traditional method.With the increase of Nd content,the thermionic emission current density increases from 11 to 16.30 A/cm2 and the magnetic phase transition temperature increases from 5.85 to 7.95 K.Thus,the SPS technique is a suitable method to synthesize the dense rare-earth hexaborides with excellent properties.     

Ca2.9M0.1Co4O9 (M=Ag,La, Ba)复合氧化物体系的制备及电输运性能

采用柠檬酸溶胶-凝胶结合放电等离子烧结方法制备了p型Ca位掺杂的Ca2.9M0.1Co4O9(M=Ag, La, Ba)复合氧化物块体试样, 对其进行X 射线衍射(XRD)分析, 表明产物为单一物相, Ca位掺杂原子可以改变Ca2.9Co4O9多晶体的取向度, 掺杂试样取向度随着掺杂原子电负性的降低而提高|对其进行扫描电子显微镜(SEM)分析结果表明, 试样呈层状结构, 且层状结构随掺杂原子电负性降低而逐渐明显; 电性能分析结果表明, 测试温度范围内掺杂试样各温度点的电阻率随着掺杂原子电负性的降低而升高, 所有试样的载流子传输层未受影响, 导电机理未发生变化. 其中掺杂电负性最高的Ag原子的烧结体保持最低取向度的同时具有最低的电阻率, 在973 K时达6.87 mΩ·cm, 而掺杂电负性最低的Ba原子的烧结体具有高的取向度的同时具有较高的电阻率, 在973 K时达8.22 mΩ·cm.