View : 21 Download: 0

Structures and Physical Properties of BaNb_(x)S_(3) (x= 1. 0, 0. 8)

Title
Structures and Physical Properties of BaNb_(x)S_(3) (x= 1. 0, 0. 8)
Authors
배현숙
Issue Date
1993
Department/Major
대학원 화학과
Keywords
StructuresPhysical PropertiesBaNb_(x)S_(3)
Publisher
이화여자대학교 대학원
Degree
Master
Advisors
김성진
Abstract
본 연구는 BaMX_(3) (when M=Ti, Nb , X=S, when M=V, Ta , X=S, Se)물질들이 같은 구조를 가짐에도 불구하고 아주 다른 물리적 성질을 갖는 원인을 알아보기 위해 시작되었다. 본 논문에서는 BaNb_(x)S_(3)(X=1.0, 0.8)을 합성하여 x-ray diffraction magnetic susceptibility, resistivity 측정, extended Hu¨ ckel계산, solid state ^(93)Nb NMR, x-ray photoelectron spectroscopy, x-ray absorption experiment 등을 수행하여 결합 특성과 결정 구조, 산화가 상태와 전자기적 성질들을 연구하였다. 모든 화합물은 CS_(2)/N_(2) 분위기에서 800 ℃의 온도로 24시간 이상 가열하여 합성하였다. BaNbS_(3) BaTaS_(3)는 합성시 금속이 +5가인 BaM_(0.8)S_(3) (M=Nb, Ta)가 만들어지고 불순물로 MS_(2)가 만들어진다고 알려져 있지만, 본 연구에서는 BaNb_(x)S_(3)에 대해 지금까지 와는 다른 결과를 관찰하였다. BaNbS_(3) phase와 소량으로 공존하는 phase는 지금까지 알려져 왔던 unknown NbS_(2) phase가 아니라 BaNb_(2)S_(5)라는 새로운 사실을 발견하였다. BaNb_(x)S_(3)(x=1.0, 0.8)는 space group이 P6_(3)/mmc이고, 이때 hexagonal cell parameter는 BaNbS_(3)에서 a=6.8404 Å, c=5.7445 Å이며, BaNb_(0.8)S_(3)에서 a=6.8356 Å, c=5.7480 Å 이었다. 또한 BaM_(0.8)S_(3)의 경우 M의 산화가 상태가 +5가가 아님을 x-ray fitting, 연소 분석, XPS, XANES 등의 결과로 부터 확인하였으며, XPS, XANES, solid state ^(93)Nb NMR 등의 결과로 부터, BaNb_(0.8)S_(3)와 BaNbS_(3)에서 Nb의 산화가 상태는 같으며 +4 이상 +5 사이의 값을 가짐을 관찰하였다. 두 경우, Nb의 spin-orbit coupling constant가 커서 d 전자가 semiconducting state로 안정화 되며, 이때의 기저상태가 zero magnetic moment인 4-fold degenerate 상태이므로 diamagneting 성질을 띠게 된다고 결론 지어졌다.;The purpose of this study is to explain the difference in the physical properties of BaMS_(3)(M=V, Nb, Ta) systems, which have the same structure. The bonding character, structure, oxidation state and electronic properties of BaNb_(x)S_(3)(x=1.0, 0.8) are investigated using x-ray diffraction, magnetic susceptibility, resistivity measurement, extended Hu¨ ckel band calculation, solid state ^(93)Nb NMR, x-ray photoelectron spectroscopy and x-ray absorption experiment. The samples are prepared in a CS_(2)/N_(2) atmosphere at 800 ℃ for over 24 hrs. Previous researchers have reported that the compounds produced were always nonstoichiometric, BaNb_(0.8)S_(3), with unidentified MS_(2) phase, regardless of reagent ratios. However, we reached a different conclusion from previous report, that is, the unidentified peaks in the x-ray pattern were found to be those of BaNb_(2)S_(5) not NbS_(2). BaNb_(x)s_(3)(x=l.0, 0.8) systems have the P6_(3)/mmc space group. The hexagonal cell parameters are a=6.8404 Å, c=5.7445 Å for BaNbS_(3) and a=6.8356 Å, c=5.7480 Åfor BaNb_(0.8)S_(3), respectively. From x-ray fitting, combustion analysis, XPS and XANES results, we concluded that the oxidation state of BaNb_(0.8)S_(3) and BaNbS_(3) are the same, and those are in between +4 and +5. The origin of unusual electronic, magnetic properties was considered to be large spin-orbit coupling constant of Nb. The large spin-orbit coupling constant stabilizes the semiconducting state, and the ground state of this state has a 4-fold degenerate, zero magnetic moment, which leads to a diamagnetic property.
Fulltext
Show the fulltext
Appears in Collections:
일반대학원 > 화학·나노과학과 > Theses_Master
Files in This Item:
There are no files associated with this item.
Export
RIS (EndNote)
XLS (Excel)
XML


qrcode

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

BROWSE