In situ Raman spectroscopy and x-ray diffraction measurements are used to explore the structural stability of CaB6 at high pressures and room temperature. The results show no evidence of structural phase transitions u...In situ Raman spectroscopy and x-ray diffraction measurements are used to explore the structural stability of CaB6 at high pressures and room temperature. The results show no evidence of structural phase transitions up to at least 40 GPa.The obtained equation of state with smooth pressure dependencies yields a zero-pressure isothermal bulk modulus B0=170(5) GPa, which agrees well with the previous measurements. The frequency shifts for A1g, Eg, and T2g vibrational modes of polycrystalline CaB6 are obtained with pressure uploading. As the pressure increases, all the vibration modes have smooth monotonic pressure dependence. The Gr¨uneisen parameter of Eg modes is the largest, indicating its largest dependence on the volume of a crystal lattice.展开更多
In last decades, topological materials [1-3] have attracted lots of research interest. Topological Kondo insulator （TKI） [4], as an exotic quantum state, has been proposed theoretically in two hexaborides StuB6 and ...In last decades, topological materials [1-3] have attracted lots of research interest. Topological Kondo insulator （TKI） [4], as an exotic quantum state, has been proposed theoretically in two hexaborides StuB6 and YbB6, in which there is a d/f（p） band inversion at momentum point X [5]. There are lots of experimental work supporting the TKI state and metallic sur- face state in typical Kondo insulator SmB6 [6-10]. However, more and more experimental results demonstrated that YbB6 is trivial insulator at ambient pressure [11]. Under high pres- sure, the band gap of YbB6 will close and the dip band inver- sion can happen under pressure about 15 GPa [12].展开更多
In this work, in-situ CaB6 reinforced aluminum matrix composites were fabricated, and the microstructure, resistivity, microhardness and coefficient of thermal expansion (CTE) of Al-CaB6 composites were studied. It is...In this work, in-situ CaB6 reinforced aluminum matrix composites were fabricated, and the microstructure, resistivity, microhardness and coefficient of thermal expansion (CTE) of Al-CaB6 composites were studied. It is found that CaB6 compounds can be formed by reducing reaction occurred in the Al melt: . CaB6 exhibits a hexahedron morphology and distributes uniformly in the Al alloy matrix. The resistivity of Al-CaB6 composites is 3.02*10-8 Ω·m, which is close to that of pure Al and lower than that of 6063Al/Ga composites. The average microhardness of Al-CaB6 composites can reach 1270 MPa, 259.8% higher than that of pure Al. Compared to pure Al, the CTE of Al-CaB6 composites is much lower.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51572108,51632002,11504127,11674122,11574112,11474127,and11634004)the 111 Project,China(Grant No.B12011)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in University,China(Grant No.IRT 15R23)the National Found for Fostering Talents of Basic Science,China(Grant No.J1103202)
文摘In situ Raman spectroscopy and x-ray diffraction measurements are used to explore the structural stability of CaB6 at high pressures and room temperature. The results show no evidence of structural phase transitions up to at least 40 GPa.The obtained equation of state with smooth pressure dependencies yields a zero-pressure isothermal bulk modulus B0=170(5) GPa, which agrees well with the previous measurements. The frequency shifts for A1g, Eg, and T2g vibrational modes of polycrystalline CaB6 are obtained with pressure uploading. As the pressure increases, all the vibration modes have smooth monotonic pressure dependence. The Gr¨uneisen parameter of Eg modes is the largest, indicating its largest dependence on the volume of a crystal lattice.
基金supported by the National Natural Science Foundation of China(Grant Nos.11604068,and 51371010)the Fundamental Research Funds for the Central Universities
文摘In last decades, topological materials [1-3] have attracted lots of research interest. Topological Kondo insulator （TKI） [4], as an exotic quantum state, has been proposed theoretically in two hexaborides StuB6 and YbB6, in which there is a d/f（p） band inversion at momentum point X [5]. There are lots of experimental work supporting the TKI state and metallic sur- face state in typical Kondo insulator SmB6 [6-10]. However, more and more experimental results demonstrated that YbB6 is trivial insulator at ambient pressure [11]. Under high pres- sure, the band gap of YbB6 will close and the dip band inver- sion can happen under pressure about 15 GPa [12].
文摘采用廉价的工业废料硼酸钙(其主要成分为CaO和B2O3,其质量分数共计约75%,下文均简称为硼酸钙)为原料,原料中不足的硼源由B4C或硼酐取代,通过碳热还原法低成本合成CaB6粉体.实验结果表明以B4C为反应物所制备得到的CaB6粉体的转化率高于以硼酐为反应物的试样.以硼酸钙,B4C和碳为原料的CaB6粉体合成的最佳烧结工艺为1923 K保温30 min.
基金financially supported by the National Natural Science Foundation of China(No.51001065)the National Basic Research Program of China(No.2012CB82702)+3 种基金Shandong Province Natural Science Foundation(No.ZR2010EQ013)in ChinaShandong Province Foundation for Outstanding Youth Scientist(No.BS2009CL035)Independent Innovation Foundation of Shandong University(No.2010TS081)Postdoctoral Independent Innovation Foundation of Shandong Province(No.200901009)
文摘In this work, in-situ CaB6 reinforced aluminum matrix composites were fabricated, and the microstructure, resistivity, microhardness and coefficient of thermal expansion (CTE) of Al-CaB6 composites were studied. It is found that CaB6 compounds can be formed by reducing reaction occurred in the Al melt: . CaB6 exhibits a hexahedron morphology and distributes uniformly in the Al alloy matrix. The resistivity of Al-CaB6 composites is 3.02*10-8 Ω·m, which is close to that of pure Al and lower than that of 6063Al/Ga composites. The average microhardness of Al-CaB6 composites can reach 1270 MPa, 259.8% higher than that of pure Al. Compared to pure Al, the CTE of Al-CaB6 composites is much lower.
