The role of defects on the structural and magnetic properties of Nb sub(2)O sub(5)

• Published in: Journal of alloys and compounds Vol. 653; pp. 358 - 362
• Main Authors: Herval, Leonilson KS, von Dreifus, Driele, Rabelo, Adriano C, Rodrigues, Ariano D, Pereira, Ernesto C, Gobato, Yara G, de Oliveira, Adilson JA, de Godoy, Marcio PF
• Format: Journal Article
• Language: English
• Published: 25.12.2015
• Subjects: Alloys; Anharmonicity; Annealing; Constants; Defects; Fingerprints; Oxygen; Vacancies
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2015.09.019

Defects play a fundamental issue on physical properties of wide bandgap materials. We present here the effect of preparation and annealing conditions on the properties of Nb sub(2)O sub(5) synthesized by Pechini method. Structural characterization, Raman spectroscopy and magnetic measurements show significant experimental fingerprints related to the presence of oxygen defects in the system. The increase of oxygen vacancies causes an irreversible phase transition from pseudohexagonal (TT-phase) to orthorhombic phase (T-phase). The critical temperature range around 400 degree C during thermal annealing is derived by in-situ Raman measurements applying the theory of phonon anharmonicity. We observed that the values of Nb sub(2)O sub(5) Curie constants as (4.37 plus or minus 0.06)10 super(-4) emu K/mol and (20.50 plus or minus 0.08)10 super(-4) emu K/mol for TT- and T-phases respectively. The oxygen vacancies are the responsible for 10 super(21)-10 super(22) effective magnetic moments per mol related to paramagnetic behavior.