Ferroelectric ceramics attracted an increasing interest due to their unique properties and wide use in many devices. Ferroelectricity arises from long-range ordering of elemental dipoles, which determines the appearance of a macroscopic polarization, while by confining the system in a small volume, a disturbance of the polar order is produced, which causes the disappearance of ferroelectric order. Up-to-date existing data indicate a critical grain size (GS) of ~10 nm for ceramic materials and a critical thickness of 2 − 3 nm in the case of epitaxial thin films. While in the case of pure BaTiO₃ (BT) ceramics, the size-dependent properties have been extensively studied, the effect of GS on the functional properties of BT-based solid solutions has only recently been addressed. These studies reported only some limited ranges for GSs and a systematic study of size effect on the dielectric, ferroelectric and dc-tunability properties of such solid solutions with GSs from 100 nm to tens of micrometers has never been performed.

In the present project we propose to prepare and investigate the functional properties from mesoscale to macroscale of BaM_xTi_1-xO₃ ceramics (M = Zr / Hf / Ge / Ce) with GS from nm to tens of μm, to elucidate if a critical size exists with enhanced dielectric/ferroelectric properties and to understand the role of intrisic/extrinsic contributions to functional properties in nanostructured dense BaM_xTi_1-xO₃ ceramics.

Project leader: asist. univ. dr. ing. Vlad-Alexandru Lukacs
Mentor: conf. univ. dr. habil. Lavinia-Petronela Curecheriu

The main objective of this project is to use a complex experimental approach to search an optimum size and to understand the role of grain size on functional properties (dielectric/ferroelectic/dc-tunabiolty) of Ba-based ferroelectric ceramics. While the previous studies based on a material science approach were focused to the size effects on dielectric and piezoelectric properties of BaTiO3 with limited GSs for applications as passive componens, the novelty of the present approach consists in a fundamental experimental study of grain size dependent phenomena in BaM_xTi_1-xO₃ ceramics (i) at nanoscale (properties decay) and (ii) searching for a critical grain size range providing enhanced dielectric/piezoelectric properties.

The specific objectives are:

1. The search for a critical grain size with enhanced functional properties in BaM_xTi_1-xO₃ ceramics (two types of homovalent substitutions).
2. The study of size dependent properties in dense BaM_xTi_1-xO₃ nanocrystalline ceramics. Two types of problems will be approached: 2.1. Obtaining dense nanocristalline BaM_xTi_1-xO₃ ceramics with controlled GS; 2.2. Role of reducing GS on the functional properties of BaM_xTi_1-xO₃ ceramics.

Raport stiintific 2022

Oral presentations at international conferences:

V.A. Lukacs, L.P. Curecheriu, L. Padurariu, L. Mitoseriu, Grain size effects on the functional properties of BaTiO3-based ceramic systems, 14th International Conference on Physics of Advanced Materials, 08-15 septembrie 2022, Dubrovnik, Croația.