Effects of Cr substitution and oxygen reduction on elastic anomaly and ultrasonic velocity incharge-ordered Nd0.5Ca0.5Mn1-xCrxO3-d ceramics
Charge-ordered Nd0.5Ca0.5Mn1-xCrxO3-d ceramics have been investigated by electrical resistivity ,AC susceptibility and ultrasonic velocity measurements to elucidate the effect so fCr substitution and oxygen reduction on charge ordering (CO). Resistivity and susceptibility measurements showed that th...
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| Main Authors: | , , |
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| Format: | Article |
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Elsevier
2013
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| Online Access: | http://dx.doi.org/10.1016/j.ceramint.2012.10.059 http://dx.doi.org/10.1016/j.ceramint.2012.10.059 http://eprints.uthm.edu.my/8162/1/dr_suhadir_2.pdf |
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| Summary: | Charge-ordered Nd0.5Ca0.5Mn1-xCrxO3-d ceramics have been investigated by electrical resistivity ,AC susceptibility and ultrasonic velocity measurements to elucidate the effect so fCr substitution and oxygen reduction on charge ordering (CO). Resistivity and susceptibility measurements showed that the x¼0 sample exhibits insulating behavior and ananti-ferromagnetic transitionat 230Kas well as a CO transitionat 280K. The substitution of Crinducesaferromagnetic–paramagneticandmetal–insulator (MI) transitionas well as gradually suppressing the CO state due to weakening of the Jahn–Teller (JT) effect. Quenching to reduce the oxygen content of the x¼0.05 sample caused the MI transition temperature to shift to lower temperatures most likely due to oxygen reduction. On the other hand, both longitudinal and shear velocities at 100K increased significantly with Cr substitution indicating improvement in elastic properties. However,quenching the x¼0.05 ample slightly deceased both velocities and related elastic moduli. A step-like longitudinal
velocity nomaly characterized by as lope change suggests the existence of CO state for x¼0, 0.02 and 0.05 samples.The step-like anomaly shifts to lower temperatures from 266K(x¼0) to222K(x¼0.05) with Cr substitution indicating aweakening of the CO state.
Absence of the step-like a nomaly for the quenched x¼0.05 sample suggests suppression of the CO state due to oxygen reduction.
Analysis of the step-like anomaly using the mean-field theory suggests involvement of the JT effect which transforms from dynamic to static type with decreasing temperature. Cr substitution weakened the CO state as are sult of weakening the JT effect while reducing the
oxygen content suppresses the CO stateasa result of oxygen reduction. |
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