Low temperature sintering of iron-barium co-doping bismuth sodium titanate lead free piezoelectric

Description

This work reports a detailed study of the crystal structure and electrical properties of a potential lead-free piezoelectric Bi0.5Na0.5TiO3 co-doped with Ba2+ and Fe3+ sintered at relatively low temperature (900 °C). The effect that co-dopants have over the electric properties in (Bi0.5Na0.5)1-xBaxTi1-yFeyO3-0.5y, varying x from 0 to 0.075, x=0.025, and y from 0 to 0.075, y=0.025, was evaluated. XRD analysis showed a successful synthesis of co-doped BNT ceramics with a rhombohedral structure for samples with x < 0.075. In contrast, the sample with x = 0.075 exhibited the coexistence of the rhombohedral and tetragonal structures, confirmed by Rietveld refinement. The co-doping promotes the grain size growth and increase the pellets’ density from 93% to 98%. Dielectric spectroscopy analysis, conducted in the range from 25 to 500 °C, showed an increase in the relative permittivity with the dopant concentration, specifically at high temperatures. Electric analysis validate the piezoelectric behavior and the electric polarization of the co-doped BNT ceramics, unveiling a maximum remnant polarization (Pr) of 25.6 µC/cm2 and, a maximum piezoelectricity coefficient of 53 pC/N, which varied depending on the composition. The obtained results demonstrate that co-doping BNT ceramics with Ba2+ and Fe3+ cations lower the sintering temperature typically used in the solid-state reaction to obtain pure BNT, showing similar properties compared to those of the same material sintered at higher temperatures and longer times.

Steps to reproduce

A specific stoichiometry was selected as a mechanism to compensate the charges, according to the composition (Bi0.5Na0.5)1-xBaxTi1-yFeyO3-0.5y where x = 0.025, 0.05 and 0.075 and y= 0.025, 0.05 and 0.075. High-purity oxide powders Fe2O3 (99.8%), TiO2 (99.6%), Bi2O3 (99.8%), and carbonates Na2CO3 (99.6 %), Ba2CO3 (99%) were used as precursors. ((1-x) 0.5)/2 〖Bi〗_2 O_3+ 1-y TiO_2+〖((1-x) 0.5)/2 Na〗_2 CO_3+y/2 〖〖Fe〗_2 O_3+x Ba〗_2 〖CO〗_3→(〖Bi〗_0.5 〖Na〗_0.5 )_(1-x) 〖Ba〗_x 〖Ti〗_(1-y) 〖Fe〗_y O_(3-0.5y)+((1-x) 0.5)/2+x 〖CO〗_(2 )↑ ( eq. 1) A total of 5 g of the mixture, along with steel balls of ½ inches whit a ball-to-powder weight ratio of 10:1, was loaded into a steel vial at room temperature and air atmosphere following the previous procedure for synthesize advanced ceramics materials [30-31]. Subsequently, the mixture was milled by means of a shaker mixer mill (SPEX model 8000D) for 5 h. After that, the powder was pressed using a hydraulic press, applying 1000 MPa for 15 minutes to obtain pellets of 10 mm in diameter. The pellets were sintered at 900 °C for 4 h using a tubular muffle furnace (Lindberg Blue) in an air atmosphere. In order to facilitate the interpretation, a specific nomenclature was used as follows: BTN-xB-yF, where x and y refer to the molar content of Ba and Fe, respectively. The phases and crystal structure were determined by X-Ray Diffraction (XRD) using a diffractometer INEL Equinox 2000 with CoKα1 radiation (λ=1.7018 Å). XRD patterns were measured in a 2ϴ range from 20 to 100, followed by Rietveld refinement using MAUD software. The crystallographic PDF data was obtained from Crystallography Open Database (COD). FEI Quanta FEG 250 scanning electron microscope (SEM) was used to examine the microstructure of the sintered pellets. The densities of sintered pellets (ρ) were determined at room temperature by Archimedes method using an AB104-S Mettler-Toledo balance, following the eq. 2: ρ=[A/(A-B) (ρ_l-ρ_a )]+ρ_a (eq. 2) Where A and B refers to the mass of the pellet in air and immersed in water, respectively, whereas ρ_l and ρ_a corresponds to the density of the reference liquid (water) and air. The pellets were painted on both surfaces with silver paste for electric characterization, determining the relative permittivity, loss tangent and electric conductivity at room temperature and as a function of temperature from 25 °C to 500°C by means of LCR Hioki 3532-50 at the frequency range from 50 to 5×106 Hz. Ferroelectric hysteresis loops were obtained at room temperature using a ferroelectric RT66B-4kV-HVi workstation (Radiant Technologies) at 10 Hz. Finally, to determine the piezoelectric constant (d33), the sintered pellets were subjected to poling under a DC field of 4.5 kV/mm at room temperature. After that, the d33 was measured 24 hours after the poling process using a d33-meter (APC International).

Institutions

• Universidad Nacional Autonoma de Mexico

  Distrito Federal, Coyoacan
• Universidad Autonoma del Estado de Hidalgo

  Pachuca
• Instituto Politecnico Nacional

  Distrito Federal, Ciudad de Mexico

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