摘要
Quasi one-dimensional polycrystalline samples of Ba_(3)Hf(Se_(1-x)Te_(x))_(5)(x=0-1)are synthesized under hightemperature and high-pressure conditions.Using the powder x-ray diffraction technique and first-principles calculations,Ba_(3)HfSe_(5)is identified as having a hexagonal structure with a space group of P63/mcm(193)and lattice constants of a=9.5756(1)A°,c=6.3802(7)A°.The structure is composed of Hf(Se1)6 chains and Se_(2)linear chains extending along the c-axis.As the doping content of Te increases,the lattice expands and leads to 5.8%and 7.3%increases of the a and c values and a 20.1%increase of the unit cell volume of Ba_(3)HfTe_(5)compared to Ba_(3)HfSe_(5).The detailed structural refinements show that the Hf vacancies decrease gradually as Te doping increases in the Ba_(3)Hf(Se_(1-x)Te_(x))_(5)(x=0-1)materials,which leads to a decrease of electronic localization.In addition,the lower electronegativity of Te and the more extended orbitals with respect to Se contribute to orbital overlap between the inter chains.All these dominate the enhanced electron hopping,leading to a reduction of the bandgap from 1.95 eV to 0.23 eV for Ba_(3)Hf(Se_(1-x)Te_(x))_(5)(x=0-1)materials as the Ba_(3)HfSe_(5)evolves to Ba_(3)HfTe_(5).
基金
supported by the National Key R&D Program of China(Grant Nos.2023YFA1406001 and 2024YFA1408004)
the National Natural Science Foundation of China(Grant Nos.12104488 and 12474097).
