Based on first-principles simulations,we revisit the crystal structures,electronic structures,and structural stability of the layered transition metal dichalcogenides(TMDCs)NbS2,and shed more light on the crucial role...Based on first-principles simulations,we revisit the crystal structures,electronic structures,and structural stability of the layered transition metal dichalcogenides(TMDCs)NbS2,and shed more light on the crucial roles of the van der Waals(vdW)interactions.Theoretically calculated results imply that the vdW corrections are important to reproduce the layered crystal structure,which is significant to correctly describe the electronic structure of NbS2.More interestingly,under hydrostatic pressure or tensile strain in ab plane,an isostructural phase transition from two-dimensional layered structure to three-dimensional bulk in the I4/mmm phase has been uncovered.The abnormal structural transition is closely related to the electronic structure instability and interlayer bonding effects.The interlayer Nb-S distances collapse and the interlayer vdW interactions disappear,concomitant with new covalent bond emerging and increasing coordination number.Present work highlights the significance of the vdW interactions,and provides new insights on the unconventional structural transitions in NbS2,which will attract wide audience working in the hectic field of TMDCs.展开更多
The oxysulfide La3NbS2O5 was synthesized by sulfurization using H2S and characterized by X-ray diffraction （XRD）, UV-Vis diffuse reflectance spectroscopy （DRS） and field emission scanning electron microscopy （FE-...The oxysulfide La3NbS2O5 was synthesized by sulfurization using H2S and characterized by X-ray diffraction （XRD）, UV-Vis diffuse reflectance spectroscopy （DRS） and field emission scanning electron microscopy （FE-SEM）. The relationship between the sulfurization conditions and the photocatalytic activities for H2 evolution was investigated. Sulfurization method allowed for synthesis of La3NbS2O5 at much lower temperatures and significantly shortened reaction time of 1 h compared with conventional solid-state techniques. The particle morphologies were regular platelike with sizes of 0.1-0.6μm and smooth surfaces. The highest activity for H2 evolution was obtained at 1073 K for 1 h, which was about 1.83 times that of La3NbS2O5 prepared by solid-state method.展开更多
Ba(Mg1/3Nb2/3)O3(BMN)复合钙钛矿陶瓷具有高介电常数和高品质因子等介电性能,预示了其在光学领域的应用前景.本文采用第一性原理方法计算了BMN的电子结构,对其本征光学性能进行分析和预测.对固相合成六方相BMN的XRD测试结果进行Rietvel...Ba(Mg1/3Nb2/3)O3(BMN)复合钙钛矿陶瓷具有高介电常数和高品质因子等介电性能,预示了其在光学领域的应用前景.本文采用第一性原理方法计算了BMN的电子结构,对其本征光学性能进行分析和预测.对固相合成六方相BMN的XRD测试结果进行Rietveld精修(加权方差因子Rwp=6.73%,方差因子Rp=5.05%),在此基础上建立晶体结构模型并对其进行几何优化.运用基于密度泛函理论(DFT)的平面波赝势方法,对六方相BMN晶体模型的能带、态密度和光学性质进行理论计算.结果表明BMN的能带结构为间接带隙,禁带宽度Eg=2.728 e V.Mg-O和Ba-O以离子键结合为主,Nb-O以共价键结合为主,费米面附近的能带主要由O-2p和Nb-4d态电子占据,形成了d-p轨道杂化.修正带隙后,计算了BMN沿[100]和[001]方向上的复介电函数、吸收系数和反射率等光学性质.结果表明,BMN近乎光学各向同性,在可见光区,其本征透过率为77%<T<83%,折射率为1.91<n<2.14,并伴随一定的色散现象.实验测试结果与理论计算结果相吻合.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11864008)Guangxi Natural Science Foundation,China(Grant Nos.2018GXNSFAA138185 and 2018AD19200)High performance computational resources provided by LvLiang Cloud Computing Center of China and National Supercomputer Center on TianHe-2 are gratefully acknowledged.
文摘Based on first-principles simulations,we revisit the crystal structures,electronic structures,and structural stability of the layered transition metal dichalcogenides(TMDCs)NbS2,and shed more light on the crucial roles of the van der Waals(vdW)interactions.Theoretically calculated results imply that the vdW corrections are important to reproduce the layered crystal structure,which is significant to correctly describe the electronic structure of NbS2.More interestingly,under hydrostatic pressure or tensile strain in ab plane,an isostructural phase transition from two-dimensional layered structure to three-dimensional bulk in the I4/mmm phase has been uncovered.The abnormal structural transition is closely related to the electronic structure instability and interlayer bonding effects.The interlayer Nb-S distances collapse and the interlayer vdW interactions disappear,concomitant with new covalent bond emerging and increasing coordination number.Present work highlights the significance of the vdW interactions,and provides new insights on the unconventional structural transitions in NbS2,which will attract wide audience working in the hectic field of TMDCs.
基金Projects(11JJ3020,10JJ9015)supported by Hunan Provincial Natural Science Foundation of ChinaProject supported by the Construct Program of the Key Discipline in Hunan Province,China
文摘The oxysulfide La3NbS2O5 was synthesized by sulfurization using H2S and characterized by X-ray diffraction （XRD）, UV-Vis diffuse reflectance spectroscopy （DRS） and field emission scanning electron microscopy （FE-SEM）. The relationship between the sulfurization conditions and the photocatalytic activities for H2 evolution was investigated. Sulfurization method allowed for synthesis of La3NbS2O5 at much lower temperatures and significantly shortened reaction time of 1 h compared with conventional solid-state techniques. The particle morphologies were regular platelike with sizes of 0.1-0.6μm and smooth surfaces. The highest activity for H2 evolution was obtained at 1073 K for 1 h, which was about 1.83 times that of La3NbS2O5 prepared by solid-state method.
文摘Ba(Mg1/3Nb2/3)O3(BMN)复合钙钛矿陶瓷具有高介电常数和高品质因子等介电性能,预示了其在光学领域的应用前景.本文采用第一性原理方法计算了BMN的电子结构,对其本征光学性能进行分析和预测.对固相合成六方相BMN的XRD测试结果进行Rietveld精修(加权方差因子Rwp=6.73%,方差因子Rp=5.05%),在此基础上建立晶体结构模型并对其进行几何优化.运用基于密度泛函理论(DFT)的平面波赝势方法,对六方相BMN晶体模型的能带、态密度和光学性质进行理论计算.结果表明BMN的能带结构为间接带隙,禁带宽度Eg=2.728 e V.Mg-O和Ba-O以离子键结合为主,Nb-O以共价键结合为主,费米面附近的能带主要由O-2p和Nb-4d态电子占据,形成了d-p轨道杂化.修正带隙后,计算了BMN沿[100]和[001]方向上的复介电函数、吸收系数和反射率等光学性质.结果表明,BMN近乎光学各向同性,在可见光区,其本征透过率为77%<T<83%,折射率为1.91<n<2.14,并伴随一定的色散现象.实验测试结果与理论计算结果相吻合.
