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Phase transitions in Ca2-xBaxNdSbO6 complex perovskites: A combined crystallographic and vibrational investigation

Abstract

An investigation into the crystal structures and vibrational degrees of freedom depending on a compositionally altered A-site chemistry are performed for the complex perovskites Ca2-xBaxNdSbO6 (0 ≤ x ≤ 2) in order to study the sequence of phase transitions and changes in the local coordination environment. The X-ray crystallographic investigations show that the samples ‘toggle’ between the pure states of monoclinic Ca2NdSbO6 (CNS) and rhombohedral Ba2NdSbO6 (BNS) with changes in composition. A novel observation is made from the crystallographic results which display a crystallographic site swapping of the Nd3+ ion when the structure transforms from CNS to BNS. The degree of this conformational site swapping of the Nd3+ has been correlated to the Ca/Ba size ratio at the A site of the perovskite lattice. The Raman spectra of the series Ca2-xBaxNdSbO6 shows remarkable signatures of a discontinuous monoclinic-rhombohedral phase transformation. A high temperature Raman analysis is carried out between 303 K and 673 K to explain the presence of a nearby rhombohedral (R3 @#x0305;)-cubic (Fm3 @#x0305;m) phase boundary. The thermal variations of the Raman spectra show a quasi-harmonic nature owing to the presence of weak rhombohedral distortion which is not effective in activating a change in the Raman profile.

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Publication details

The article was received on 26 Feb 2019, accepted on 10 May 2019 and first published on 10 May 2019


Article type: Paper
DOI: 10.1039/C9CE00275H
CrystEngComm, 2019, Accepted Manuscript

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    Phase transitions in Ca2-xBaxNdSbO6 complex perovskites: A combined crystallographic and vibrational investigation

    S. Halder and T. P. Sinha, CrystEngComm, 2019, Accepted Manuscript , DOI: 10.1039/C9CE00275H

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