Structure and phase transitions in niobium and tantalum derived nanoscale transition metal perovskites, Ba(Ti,MV)O3, M=Nb,Ta

Julien Lombardi; Long Yang; Nasim Farahmand; Anthony Ruffino; Ali Younes; Jonathan E Spanier; Simon J L Billinge; Stephen O'Brien

doi:10.1063/5.0192488

Structure and phase transitions in niobium and tantalum derived nanoscale transition metal perovskites, Ba(Ti,MV)O3, M=Nb,Ta

J Chem Phys. 2024 Apr 7;160(13):134702. doi: 10.1063/5.0192488.

Authors

Julien Lombardi^{1

2

3}, Long Yang⁴, Nasim Farahmand^{1

2

3}, Anthony Ruffino⁵, Ali Younes⁶, Jonathan E Spanier^{5

7}, Simon J L Billinge⁸, Stephen O'Brien^{1

2

3}

Affiliations

¹ The CUNY Energy Institute, City University of New York, Steinman Hall, 160 Convent Avenue, The City College of New York, New York, New York 10031, USA.
² Department of Chemistry and Biochemistry, The City College of New York, 1024 Marshak, 160 Convent Avenue, New York, New York 10031, USA.
³ Ph.D. Program in Chemistry, The Graduate Center, The City University of New York, New York, New York 10016, USA.
⁴ School of Materials Science and Engineering, Tongji University, 4800 Caoan Road, Shanghai 201804, China.
⁵ Department of Physics, Drexel University, Philadelphia, Pennsylvania 19104, USA.
⁶ Department of Chemistry, Hunter College of the City University of New York, 695 Park Ave., New York, New York 10065, USA.
⁷ Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, Pennsylvania 19104, USA.
⁸ Department of Applied Physics and Applied Mathematics, Columbia University, 500 West 120th Street, New York, New York 10027, USA.

PMID: 38573849
DOI: 10.1063/5.0192488

Abstract

The prospect of creating ferroelectric or high permittivity nanomaterials provides motivation for investigating complex transition metal oxides of the form Ba(Ti, MV)O3, where M = Nb or Ta. Solid state processing typically produces mixtures of crystalline phases, rarely beyond minimally doped Nb/Ta. Using a modified sol-gel method, we prepared single phase nanocrystals of Ba(Ti, M)O3. Compositional and elemental analysis puts the empirical formulas close to BaTi0.5Nb0.5O3-δ and BaTi0.5Ta0.5O3-δ. For both materials, a reversible temperature dependent phase transition (non-centrosymmetric to symmetric) is observed in the Raman spectrum in the region 533-583 K (260-310 °C); for Ba(Ti, Nb)O3, the onset is at 543 K (270 °C); and for Ba(Ti, Ta)O3, the onset is at 533 K (260 °C), which are comparable with 390-393 K (117-120 °C) for bulk BaTiO3. The crystal structure was resolved by examination of the powder x-ray diffraction and atomic pair distribution function (PDF) analysis of synchrotron total scattering data. It was postulated whether the structure adopted at the nanoscale was single or double perovskite. Double perovskites (A2B'B″O6) are characterized by the type and extent of cation ordering, which gives rise to higher symmetry crystal structures. PDF analysis was used to examine all likely candidate structures and to look for evidence of higher symmetry. The feasible phase space that evolves includes the ordered double perovskite structure Ba2(Ti, MV)O6 (M = Nb, Ta) Fm-3m, a disordered cubic structure, as a suitable high temperature analog, Ba(Ti, MV)O3Pm-3m, and an orthorhombic Ba(Ti, MV)O3Amm2, a room temperature structure that presents an unusually high level of lattice displacement, possibly due to octahedral tilting, and indication of a highly polarized crystal.