Nontrivial topological behaviors in superconducting materials provide resourceful ground for the emergence and study of unconventional quantum states.Charge doping by the controlled intercalation of donor atoms is an ...Nontrivial topological behaviors in superconducting materials provide resourceful ground for the emergence and study of unconventional quantum states.Charge doping by the controlled intercalation of donor atoms is an efficient route for enhancing/inducement of superconducting and topological behaviors in layered topological insulators and semimetals.Herein,we enhanced the superconducting temperature of TaSe_(2) by 20-folds(~3 K)through Sn atoms intercalation.Using first-principles calculations,we demonstrated the existence of nontrivial topological features.Sn_(0.5)TaSe_(2) displays topological nodal lines around the K high symmetry point in the Brillouin zone,with drumhead-like shaped surface states protected by inversion symmetry.Altogether,the coexistence of these properties makes Sn_(0.5)TaSe_(2) a potential candidate for topological superconductivity.展开更多
The possible defect models of Y^3＋：PbWO4 crystals are discussed by defect chemistry and the most possible substituting positions of the impurity Y^3＋ ions are studied by using the general utility lattice program （...The possible defect models of Y^3＋：PbWO4 crystals are discussed by defect chemistry and the most possible substituting positions of the impurity Y^3＋ ions are studied by using the general utility lattice program （GULP）. The calculated results indicate that in the lightly doped Y^3＋ ：PWO crystal, the main compensating mechanism is [2Ypb^＋ ＋ VPb^2-], and in the heavily doped Y^3＋ ：PWO crystal, it will bring interstitial oxygen ions to compensate the positive electricity caused by YPb^＋, forming defect clusters of [2Ypb^＋ ＋Oi^2-] in the crystal. The electronic structures of Y3＋ ：PWO with different defect models are calculated using the DV-Xα method. It can be concluded from the electronic structures that, for lightly doped cases, the energy gap of the crystal would be broadened and the 420nm absorption band will be restricted; for heavily doped cases, because of the existence of interstitial oxygen ions, it can bring a new absorption band and reduce the radiation hardness of the crystal.展开更多
We report the effects of post-thermal treatment on the quality of 2-inch 6H-SiC wafer cut from a crystal boule grown by physical vapour transportation method. The full widths at half maximum of x-ray diffraction rocki...We report the effects of post-thermal treatment on the quality of 2-inch 6H-SiC wafer cut from a crystal boule grown by physical vapour transportation method. The full widths at half maximum of x-ray diffraction rocking curves measured on sites across the 2-inch wafer become narrower, indicating the quality improvement after a three-step post-thermal treatment. It is found that the most common defects such as micropipes and inclusions can be significantly reduced after the treatment. Our results show that the post-thermal treatment is an effective route to improve the quality of SiC single crystals.展开更多
Electronic structures of PbWO4 crystals containing F-type colour centres with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Dirac-Slater theory, using a num...Electronic structures of PbWO4 crystals containing F-type colour centres with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Dirac-Slater theory, using a numerically discrete variational （DV-Xα） method. The calculated results show that F and F^＋ centres have donor energy levels in the forbidden bands. Their optical transition energies are 1.84 eV and 2.21 eV, respectively, which correspond to the 680nm and 550 nm absorption bands. It is predicted that the 680 nm and 550nm absorption banas originate from the F and F^＋ centres in PbWO4 crystals.展开更多
High quality Sr14-xCaxCu24O41 single-crystals are successfully grown by floating-zone technique, and the trans- port properties are studied. The temperature dependence of resistivity along the c-axis direction is semi...High quality Sr14-xCaxCu24O41 single-crystals are successfully grown by floating-zone technique, and the trans- port properties are studied. The temperature dependence of resistivity along the c-axis direction is semiconductor- like for x ≤ 10 and it can be fitted by the thermal activation equation p = po exp（ △ /kBT） with kB being the Boltzmann constant and A the activation energy. A break in the slope of thermopower （S） versus the inverse temperature （1 IT） corresponding to the formation of charge-density waves （CD W） is first observed for x ≤ 6. The temperature dependence of thermopower becomes metallic for x ≥ 8 while the resistivity is still semiconductorlike. We propose that the insulation behaviour of the resistivity in the Ca doping range 8 ≤ x ≤ 11 could result from the localization of the charge carriers due to the disorder induced by Ca doping and a revised electronic phase diagram is derived based on our observations.展开更多
Non-stoichiometric Ni50Mn27 Ga23 polycrystalline ribbons are prepared by melt-spinning technique. The magneticfield-induced strain （MFIS） of Ni-Mn-Ga bulk alloy prepared by bonding the melt-spun ribbons is obtained....Non-stoichiometric Ni50Mn27 Ga23 polycrystalline ribbons are prepared by melt-spinning technique. The magneticfield-induced strain （MFIS） of Ni-Mn-Ga bulk alloy prepared by bonding the melt-spun ribbons is obtained. The experimental results show that Ni50Mn27Ga23 bonded ribbons exhibit a typical thermal-elastic shape memory effect in the thickness direction. The martensitic transformation strain of bonded ribbons is an expansive strain of about 0.3% without the magnetic field and a contractive strain of about -0.46% at the magnetic field of 1 T. The field can not only enhance the value of the martensitic transformation strain of the bonded ribbons, but can also change the direction of the strain. The bonded ribbons alloy presents negative MFIS and obtains a larger value of the strain though influenced by the adhesive between the ribbons. Therefore, the preparation technique of the Ni-Mn-Ga bulk alloy by bonding melt-spun ribbons is helpful to get rid of the size restriction of the ribbon and to broaden the applications of the ribbons.展开更多
Taking advantage of the unique layered structure of TiSe2,the intrinsic electronic properties of two-dimensional materials can easily be tuned via heteroatomic engineering.Herein,we show that the charge density wave(C...Taking advantage of the unique layered structure of TiSe2,the intrinsic electronic properties of two-dimensional materials can easily be tuned via heteroatomic engineering.Herein,we show that the charge density wave(CDW)phase in 1T-TiSe_(2) single-crystals can be gradually suppressed through Sn atoms intercalation.Using angle-resolved photoemission spectroscopy(ARPES)and temperature-dependent resistivity measurements,this work reveals that Sn atoms can induce charge doping and modulate the intrinsic electronic properties in the host 1T-TiSe_(2).Notably,our temperature-dependent ARPES results highlight the role exciton-phonon interaction and the Jahn-Teller mechanism through the formation of backfolded bands and exhibition of a downward Se shift of 4p valence band in the formation of CDW in this material.展开更多
By the nonlinear optimization theory, we predict the yield function of single BCC crystals in Hill＇s criterion form. Then we give a formula on the macroscopic yield function of a BCC polycrystal Ω under Sachs＇ mode...By the nonlinear optimization theory, we predict the yield function of single BCC crystals in Hill＇s criterion form. Then we give a formula on the macroscopic yield function of a BCC polycrystal Ω under Sachs＇ model, where the volume average of the yield functions of all BCC crystallites in Ω is taken as the macroscopic yield function of the BCC polycrystal. In constructing the formula, we try to find the relationship among the macroscopic yield function, the orientation distribution function （ODF）, and the single BCC crystal＇s plasticity. An expression for the yield stress of a uniaxial tensile problem is derived under Taylor＇s model in order to compare the expression with that of the macroscopic yield function.展开更多
Relaxor ferroelectric single crystals PMNT with the size of φ40 mm×80 mm have been grown by a modified Bridgman method and their ferroelectric and piezoelectric properties have been characterized. The properties...Relaxor ferroelectric single crystals PMNT with the size of φ40 mm×80 mm have been grown by a modified Bridgman method and their ferroelectric and piezoelectric properties have been characterized. The properties varied with the compositions and cut types. On the (001) cut, PMNT76/24 single crystals exhibited a dielectric constant ε of about 3 400, a dielectric loss of tanδ 【0.7%, a piezoelectric constant d33 of 980 pC/N, an electromechanical coupling factor kt of 0.55 and Tc of about 110℃. whereas the properties of PMNT67/33 single crystals on (001) cut were betler: e of about 5 300, tan5 【0.6%, d33 up to 3 000 pC/N, kt 0.64, K33 0.93 and Tc of about 150℃. The piezoelectric properties on other cuts such as (110) and (111) were much lower than those on the (001) cut. The rhombohedral PMNT crystals grown by this method showed more excellent piezoelectric properties than those grown by high temperature solution method and higher value of kt than the rhombohedral PZNT single crystals. it has also展开更多
基金the financial support in part by the National Key R&D Program of China(No.2017YFA0303500)the National Natural Science Foundation of China(NSFC)(Nos.U1932201,11574280,and 21727801)+2 种基金NSFC-MAECI(No.51861135202)International Partnership Program of CAS(No.211134KYSB20190063)CAS Collaborative Innovation Program of Hefei Science Center(No.2019HSC-CIP002).
文摘Nontrivial topological behaviors in superconducting materials provide resourceful ground for the emergence and study of unconventional quantum states.Charge doping by the controlled intercalation of donor atoms is an efficient route for enhancing/inducement of superconducting and topological behaviors in layered topological insulators and semimetals.Herein,we enhanced the superconducting temperature of TaSe_(2) by 20-folds(~3 K)through Sn atoms intercalation.Using first-principles calculations,we demonstrated the existence of nontrivial topological features.Sn_(0.5)TaSe_(2) displays topological nodal lines around the K high symmetry point in the Brillouin zone,with drumhead-like shaped surface states protected by inversion symmetry.Altogether,the coexistence of these properties makes Sn_(0.5)TaSe_(2) a potential candidate for topological superconductivity.
文摘The possible defect models of Y^3＋：PbWO4 crystals are discussed by defect chemistry and the most possible substituting positions of the impurity Y^3＋ ions are studied by using the general utility lattice program （GULP）. The calculated results indicate that in the lightly doped Y^3＋ ：PWO crystal, the main compensating mechanism is [2Ypb^＋ ＋ VPb^2-], and in the heavily doped Y^3＋ ：PWO crystal, it will bring interstitial oxygen ions to compensate the positive electricity caused by YPb^＋, forming defect clusters of [2Ypb^＋ ＋Oi^2-] in the crystal. The electronic structures of Y3＋ ：PWO with different defect models are calculated using the DV-Xα method. It can be concluded from the electronic structures that, for lightly doped cases, the energy gap of the crystal would be broadened and the 420nm absorption band will be restricted; for heavily doped cases, because of the existence of interstitial oxygen ions, it can bring a new absorption band and reduce the radiation hardness of the crystal.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50132040 and 50302014, the National Basic Research Program of China, and the Knowledge Innovation Project of Chinese Academy of Sciences.
文摘We report the effects of post-thermal treatment on the quality of 2-inch 6H-SiC wafer cut from a crystal boule grown by physical vapour transportation method. The full widths at half maximum of x-ray diffraction rocking curves measured on sites across the 2-inch wafer become narrower, indicating the quality improvement after a three-step post-thermal treatment. It is found that the most common defects such as micropipes and inclusions can be significantly reduced after the treatment. Our results show that the post-thermal treatment is an effective route to improve the quality of SiC single crystals.
文摘Electronic structures of PbWO4 crystals containing F-type colour centres with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Dirac-Slater theory, using a numerically discrete variational （DV-Xα） method. The calculated results show that F and F^＋ centres have donor energy levels in the forbidden bands. Their optical transition energies are 1.84 eV and 2.21 eV, respectively, which correspond to the 680nm and 550 nm absorption bands. It is predicted that the 680 nm and 550nm absorption banas originate from the F and F^＋ centres in PbWO4 crystals.
基金Supported by the National Basic Research Programme of China under Grant No 2007CB925001, and the Natural Science Foundation of Zhejiang Province under Grant No Y605106.
文摘High quality Sr14-xCaxCu24O41 single-crystals are successfully grown by floating-zone technique, and the trans- port properties are studied. The temperature dependence of resistivity along the c-axis direction is semiconductor- like for x ≤ 10 and it can be fitted by the thermal activation equation p = po exp（ △ /kBT） with kB being the Boltzmann constant and A the activation energy. A break in the slope of thermopower （S） versus the inverse temperature （1 IT） corresponding to the formation of charge-density waves （CD W） is first observed for x ≤ 6. The temperature dependence of thermopower becomes metallic for x ≥ 8 while the resistivity is still semiconductorlike. We propose that the insulation behaviour of the resistivity in the Ca doping range 8 ≤ x ≤ 11 could result from the localization of the charge carriers due to the disorder induced by Ca doping and a revised electronic phase diagram is derived based on our observations.
文摘Non-stoichiometric Ni50Mn27 Ga23 polycrystalline ribbons are prepared by melt-spinning technique. The magneticfield-induced strain （MFIS） of Ni-Mn-Ga bulk alloy prepared by bonding the melt-spun ribbons is obtained. The experimental results show that Ni50Mn27Ga23 bonded ribbons exhibit a typical thermal-elastic shape memory effect in the thickness direction. The martensitic transformation strain of bonded ribbons is an expansive strain of about 0.3% without the magnetic field and a contractive strain of about -0.46% at the magnetic field of 1 T. The field can not only enhance the value of the martensitic transformation strain of the bonded ribbons, but can also change the direction of the strain. The bonded ribbons alloy presents negative MFIS and obtains a larger value of the strain though influenced by the adhesive between the ribbons. Therefore, the preparation technique of the Ni-Mn-Ga bulk alloy by bonding melt-spun ribbons is helpful to get rid of the size restriction of the ribbon and to broaden the applications of the ribbons.
基金the National Key R&D Program of China(Nos.2020YFA0405800 and 2017YFA0303500)the National Natural Science Foundation of China(NSFC)(Nos.U1932201,and 21727801)+2 种基金the International Partnership Program of The Chinese Academy of Sciences(CAS)(No.211134KYSB20190063)the CAS Collaborative Innovation Program of Hefei Science Center(No.2019HSC-CIP002)the University Synergy Innovation Program of Anhui Province(No.GXXT-2020-002)。
文摘Taking advantage of the unique layered structure of TiSe2,the intrinsic electronic properties of two-dimensional materials can easily be tuned via heteroatomic engineering.Herein,we show that the charge density wave(CDW)phase in 1T-TiSe_(2) single-crystals can be gradually suppressed through Sn atoms intercalation.Using angle-resolved photoemission spectroscopy(ARPES)and temperature-dependent resistivity measurements,this work reveals that Sn atoms can induce charge doping and modulate the intrinsic electronic properties in the host 1T-TiSe_(2).Notably,our temperature-dependent ARPES results highlight the role exciton-phonon interaction and the Jahn-Teller mechanism through the formation of backfolded bands and exhibition of a downward Se shift of 4p valence band in the formation of CDW in this material.
基金Project supported by the National Natural Science Foundation of China (No. 10562004) the Natural Science Foundation of Jiangxi (Nos.0450035 and 0512021) the Science Foundation of Jiangxi Educational Department (No.[2006]3) the Oversea Returned Scholars Grant of China.
文摘By the nonlinear optimization theory, we predict the yield function of single BCC crystals in Hill＇s criterion form. Then we give a formula on the macroscopic yield function of a BCC polycrystal Ω under Sachs＇ model, where the volume average of the yield functions of all BCC crystallites in Ω is taken as the macroscopic yield function of the BCC polycrystal. In constructing the formula, we try to find the relationship among the macroscopic yield function, the orientation distribution function （ODF）, and the single BCC crystal＇s plasticity. An expression for the yield stress of a uniaxial tensile problem is derived under Taylor＇s model in order to compare the expression with that of the macroscopic yield function.
文摘Relaxor ferroelectric single crystals PMNT with the size of φ40 mm×80 mm have been grown by a modified Bridgman method and their ferroelectric and piezoelectric properties have been characterized. The properties varied with the compositions and cut types. On the (001) cut, PMNT76/24 single crystals exhibited a dielectric constant ε of about 3 400, a dielectric loss of tanδ 【0.7%, a piezoelectric constant d33 of 980 pC/N, an electromechanical coupling factor kt of 0.55 and Tc of about 110℃. whereas the properties of PMNT67/33 single crystals on (001) cut were betler: e of about 5 300, tan5 【0.6%, d33 up to 3 000 pC/N, kt 0.64, K33 0.93 and Tc of about 150℃. The piezoelectric properties on other cuts such as (110) and (111) were much lower than those on the (001) cut. The rhombohedral PMNT crystals grown by this method showed more excellent piezoelectric properties than those grown by high temperature solution method and higher value of kt than the rhombohedral PZNT single crystals. it has also
