Investigation on the phase stability and defect structure of Li-Mn-O and Li-Me-Mn-O spinel (Me=Mg, Ni, Co)

This thesis has been an effort to interpret the defect structure of the nonstoichiometric spinel. The Li-Mn-O spinel and doped Li-Me-Mn-O (Me = Mg, Co, Ni) spinel were synthesized in modified Pechini method. The phase stability was investigated by in situ XRD, TG and DTA. A new phase diagram is put forward, in which the stability region is described by upper and lower critical temperature, Tc1 and TcL. Both Tc1 and TcL decrease continuously with nLi/nMn increasing, and increase linearly with log(pO2) increasing. A three-dimensional phase diagram is put forward, in which the single phase spinel boundary is described by nLi/nMn, pO2 and temperature. Tc1 of the doped spinel is lower than that of undoped spinel with the same lithium content, and decreases with increase of the dopant concentration. Three types of cation distribution are proposed to describe the referential state of the lithium excess or lithium deficit spinel. On the basis of referential state of cation distribution the delta dependence on pO2 in (Li, Mn)3O4–delta and (Li, Me, Mn)3O4–delta is determined. The nonstoichiometry change was measured by TG as function of pO2 variation, and Deltadelta–pO2 diagram was fitted by using different defect models. It is concluded that in a lithium excess spinel, the excess Li ions substitute for Mn ions on octahedral 16d sites, of which the defect structure is explained by the combined defect model of lithium interstitials and cation vacancies with delta–pO2 dependence: delta = -b x (pO2/p0)2/3 + c x (pO2/p0)-2/3. The maximum nonstoichiometry change, Deltadeltamax, is about 0.0015, which are much smaller than that reported in literature.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2005

Author dc:creator

• Luo, Chunhui

Contributors dc:contributor

• Martin, Manfred

• info:eu-repo/classification/ddc/530
• Physik
• Spinel
• Defect
• Nonstoichiometry
• Phase diagram

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-114159%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51911