• Torrespardo, Almudena
• Ruizcaridad, Alicia
• Dezanneau, Guilhem
• Peiró, Francesca
• Rebled, José Manuel
• Estradé, Sonia
• Gonzálezcalbet, José Maria
• Ruizgonzález, Luisa
• Lópezconesa, Lluís

Abstract

<jats:p>SBN belongs to the tetragonal tungsten bronze (TTB) family of uniaxial ferroelectric relaxor materials, with a single component polarization vector pointing along the tetragonal<jats:italic>c</jats:italic>axis. The high dielectric constants observed and polarization controlling around the ordering temperature 'T<jats:sub>m</jats:sub>' make of relaxors promising systems for applications such as electrocaloric, pyroelectric, piezoelectric/electrostrictive devices and sensors.</jats:p><jats:p>The idealized structure of SBN, with the generalized formula A<jats:sub>2</jats:sub>B<jats:sub>4</jats:sub>C<jats:sub>4</jats:sub>Nb<jats:sub>2</jats:sub>Nb<jats:sub>8</jats:sub>O<jats:sub>30</jats:sub>, has three types of structural channels along the<jats:italic>c</jats:italic>axis, formed by two types of crystallographically independent NbO<jats:sub>6</jats:sub>octahedra. Disorder due to presence of voids on A cation sites (occupied by Sr atoms) and random distribution of Ba and Sr on B cation sites are thought to be responsible for the relaxor behavior, via the formation of random electric fields and, subsequently, polar nanodomains oriented in the only easy polarization axis<jats:italic>c</jats:italic>, without a structural change occurring in the phase transition. In this work we present structural and chemical studies of a SBN single crystal by means of Selected Area Electron Diffraction (SAED), High Angular Annular Dark Field (HAADF), Annular Bright Field (ABF) and Electron Energy Loss Spectroscopy (EELS) along the [001] and [100] zone axes. Experiments were carried out in non‐aberration corrected (Phillips CM30, JEOL J2100, JEOL2010F) and probe‐corrected (Titan<jats:sup>3</jats:sup>G2, ARM cF200) TEMs.</jats:p><jats:p>An incommensurate structural modulation in SAED experiments along the [100] direction already points to structural disorder (Fig. 1). Diffuse scattering in the form of streaking patterns in the main reflections can also be related to strain induced by the presence of vacant sites. HAADF imaging along the [100] zone axis directly shows in real space the presence of cationic vacancies in A‐type sites. Elongation of the atomic columns in the center of the B pentagonal sites in HAADF images along the [001] zone axis (Fig. 2) is compatible with the presence of Ba and Sr randomly occupying that crystallographic position. EELS spectrum imaging along the [001] zone axis (Fig. 3) directly confirmed the mixing of Sr/Ba in the B‐type sites. With these results, the causes for local charge disorder in the structure are mapped in direct space with atomic column resolution. ABF imaging allowed mapping the oxygen sublattice in the structure, achieving the full structural characterization of the material.</jats:p>

Topics

• impedance spectroscopy
• single crystal
• phase
• experiment
• Oxygen
• electron diffraction
• dielectric constant
• phase transition
• transmission electron microscopy
• random
• void
• tungsten
• bronze
• electron energy loss spectroscopy