Magnetic and Mössbauer Studies of the System LaCo 1− x Zr x O 3 ( x = 0.1, 0.3, 0.5)

Mössbauer studies on well‐characterized LaCo 1− x Zr x O 3 ( x = 0.1, 0.3, 0.5) are carried out in the 80 to 700 K temperature range and they show that cobalt ions exist predominantly in the low spin Co III (t   2g 6 e   g 0 ) and Co II (t   2g 6 e   g 1 ) states at 80 K which transform partially to high‐spin Co 3+ (t   2g 4 e   g 2 ) ions upto ≈ 500 K. In the 80 to 700 K region the system LaCo 0.9 Zr 0.1 O 3 behaves almost similar to LaCoO 3 . However, above 500 K, in the system LaCo 1− x Zr x O 3 ( x = 0.3, 0.5) Co 3+ ions capture an electron from Co II and transform into Co 2+ (t   2g 5 e   g 2 ) and Co III ions pairs. The magnetic susceptibility data recorded are consistent with the present Mössbauer resülts. The inverse magnetic susceptibility versus temperature curves for the systems LaCo 1− x Zr x O 3 ( x = 0.3, 0.5) show different slopes in the 300 to 800 K temperature range. The higher slopes above ≈ 500 and ≈ 550 K for the system LaCo 0.7 Zr 0.3 O 3 and LaCo 0.5 Zr 0.5 O 3 , respectively, indicate lower μ eff which, in turn, suggests the generation of Co 2+ ions at the cost of Co 3+ ions. The generation of low spin Co II and Co III at low temperatures is attributed to larger crystal field splitting Δ cf compared to exchange energy Δ ex in the system as a result of tetravalent Zr ion substitution.