Synthesis and characterisation of the vibrational and electrical properties of antiferromagnetic 6L-Ba2CoTeO6 ceramics

Anees A Aziz; Silvana Mercone; Ricardo P S M Lobo; Anderson Dias; Roberto L Moreira; Anthony M T Bell; Roger Eccleston; Antonio Feteira

doi:10.1039/c9dt00418a

Synthesis and characterisation of the vibrational and electrical properties of antiferromagnetic 6L-Ba₂CoTeO₆ ceramics

Dalton Trans. 2019 Aug 7;48(29):11112-11121. doi: 10.1039/c9dt00418a. Epub 2019 Jul 2.

Authors

Anees A Aziz¹, Silvana Mercone², Ricardo P S M Lobo³, Anderson Dias⁴, Roberto L Moreira⁵, Anthony M T Bell⁶, Roger Eccleston⁶, Antonio Feteira⁶

Affiliations

¹ Christian Doppler Lab in Advanced Ferroic Oxides, Materials and Engineering Research Institute, Sheffield Hallam University, Howard Street, Sheffield, UK. E-mail:. a.feteira@shu.ac.uk and Faculty of Electrical Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia.
² LSPM, CNRS UPR 3407, Université Paris Nord, Sorbonne Paris Cité, 99 Avenue J.-B. Clément, 93430 Villetaneuse, France.
³ LPEM, ESPCI Paris, PSL University, CNRS, F-75005 Paris, France and Sorbonne Université, CNRS, LPEM, F-75005 Paris, France.
⁴ Departamento de Química, ICEx, Universidade Federal de Minas Gerais, 30123-970 Belo Horizonte, Minas Gerais, Brazil.
⁵ Departamento de Física, ICEx, Universidade Federal de Minas Gerais, C.P. 702, 30123-970 Belo Horizonte, Minas Gerais, Brazil.
⁶ Christian Doppler Lab in Advanced Ferroic Oxides, Materials and Engineering Research Institute, Sheffield Hallam University, Howard Street, Sheffield, UK. E-mail:. a.feteira@shu.ac.uk.

PMID: 31263816
DOI: 10.1039/c9dt00418a

Abstract

Optimal processing conditions for fabrication of dense single-phase 6L-Ba₂CoTeO₆ ceramics via the solid-state reaction method were determined. These ceramics possess a room-temperature crystal structure described by the centrosymmetric P3[combining macron]m1 space group. Polarized Raman spectroscopy enabled the observation of all the 25 predicted Raman modes and assignment of their symmetries. On cooling, BCTO ceramics exhibit two antiferromagnetic transitions at 3 K and 12.5 K, in broad agreement with a recent single-crystal study [P. Chanlert, N. Kurita, H. Tanaka, D. Goto, A. Matsuo and K. Kindo, Phys. Rev. B: Condens. Matter Mater. Phys., 2016, 93, 094420]. Low temperature Fourier-transform infrared reflectivity analyses suggest the antiferromagnetic phase transitions to be driven by small distortions of the CoO₆ octahedra, lowering locally their C_3v symmetry. This causes splitting of the associated vibrational modes, but without a long-range structural change. AC impedance spectroscopy revealed BCTO ceramics to be leaky insulators with an activation energy for conduction of ∼0.15-0.25 eV, which suggests electron hopping between mixed oxidation states of Co.