Impact of metal substitutions for cobalt in YBaCo4O7

✍ Scribed by A. Maignan; V. Caignaert; V. Pralong; D. Pelloquin; S. Hébert

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 687 KB
• Volume: 181
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1016/j.jssc.2008.02.031

✦ Synopsis

The ''114'' YBaCo 4 O 7 cobaltite undergoes structural transition just beyond room temperature at T S $310 K. Correspondingly, its signature in the physical properties is detected by T-dependent measurements of electrical resistivity, magnetic susceptibility and thermoelectric power. It is found that low-level substitutions of divalent (M ¼ Zn 2+ ) or trivalent (M ¼ Ga 3+ , Al 3+ ) cations for cobalt according to the YBaCo 4Àx M x O 7 formula with xp0.4 have a strong impact upon this transition. On the one hand, Zn 2+ substitutions preserve the transition but with T S decreasing as x increases. On the other hand, for x ¼ 0.2 Ga 3+ or Al 3+ , the transition is suppressed, i.e., for only 5% trivalent foreign cation substituted for cobalt. Though at first, this contrasted behaviour between divalent and trivalent substituting cations appears to be linked to the opposite evolution of hole carriers ''Co 3+ '' concentration with x, a possible destabilization of 3Co 2+ : 1Co 3+ charge ordering induced by the M 3+ cations is considered.