D. Do

High-Performance Lead-Free Piezoceramics with High Curie Temperatures.

A bismuth ferrite and barium titanate solid solution compound can achieve good piezoelectric properties with a high Curie temperature when fabricated with low-temperature sintering followed by a water-quenching process, with no complicated grain alignment processes performed. By adding the super-tetragonal bismuth gallium oxide to the compound, the piezoelectric properties are as good as those of lead zirconate titanate ceramics.

Ferroelectric and Piezoelectric Properties of BiFeO3-BaTiO3Solid Solution Ceramics

Effects of heat-treat procedure and sintering temperatures were investigated in 0.67Bi1.05FeO3-0.33BaTiO3ceramics. The structure, dielectric, ferroelectric, and piezoelectric properties of ceramics made by normal cooling or quenched cooling process were investigated. All ceramics show single pseudo-cubic perovskite crystal structure. Although the structure was not changed but other properties were much changed by heat-treatment. The normally cooled ceramic showed ‘pinched’ ferroelectric hysteresis loops with remanent polarization value of about 10 μC/cm2. On the contrary, the quenched ceramic showed ‘normal’ ferroelectric hysteresis loops with remanent polarization value of about 17 μC/cm2. The piezoelectric constant d 33value of 13 pC/N in normally cooled ceramic was improved to 39 pC/N in quenched ceramic. These improved results were attributed to the reduced populations of defects made during the heat-treatments.

High piezoelectric performance of lead-free BiFeO3–BaTiO3 thin films grown by a pulsed laser deposition method

Lead-free (100 − x)BiFeO3–xBaTiO3 (BFBTx, x = 0, 30, 33, 40 and 50) piezoelectric thin films were deposited on platinized silicon substrates by using a pulsed laser deposition method. The BFBTx thin films has a single-phase perovskite structure with (111) preferred orientations. Atomic force microscopy images showed the dense morphology, and large piezoresponses were observed in the piezoelectric force microscope measurements. The best local piezoelectric coefficient, value of 259 pm V−1, was observed in the BFBT40 thin film. This result is one of the best values in lead-free piezoelectric thin films with a simple geometry. The BFBT40 piezoelectric thin film can be considered as a strong candidate to replace lead-based piezoelectric thin films for piezoelectric-based microelectromechanical systems.

The Effects of Mn Substitution and Oxidation States of Mn in BiFeO3 Thin Films

Multiferroic Bi(Fe0.9Mn x 0.1)O3 (x = 2+, 3+, and 4+) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a pulsed laser deposition method. The effects of different oxidation states of Mn used as a starting material on crystal structure, leakage current, dielectric, and ferroelectric properties were investigated. No significant change in the crystal structure was observed while electrical properties were affected by the oxidation states of Mn. A frequency-dependent dielectric relaxation region was observed in the films with Mn3+ and Mn2+, indicating the presence of space charges such as oxygen vacancies.

Improvement of Ferroelectric and Leakage Current Properties with Zn-Mn Co-doping in BiFeO3 Thin Films

Ferroelectric and leakage current behaviors of Zn-Mn co-doped polycrystalline BiFeO3 (BFO) thin films fabricated by a pulsed laser deposition were investigated in comparison with un-doped BFO thin films. Ferroelectric hysteresis loop was observed in Zn-Mn co-doped BFO film capacitor: 2P r = 109 μC/cm2 and 2E C = 674 kV/cm with maximum electric field of 600 kV/cm. And leakage current was reduced with Zn-Mn co-doping at low electric field region and 10 mol% Bi-excess BFO film has best leakage current behavior in a wide electric field range.

The thermal treatment effect on electrical properties of mn-modified polycrystalline BiFeO 3 thin films

Mn modified BFO (BFMO) thin films has been deposited using pulsed laser deposition on Pt(111)/Ti/SiO2/Si(100) substrates at 540°C. After completion of deposition, the BFMO thin films were cooled by two different procedures; quenching and chamber cooling. Differences in structural and electrical properties of BFMO thin films were investigated by an X-ray diffractometer and an electrical system, respectively. Improvement in ferroelectricity, a large remnant polarization of ~187.39 μC/cm2 with 600 kV/cm, was found from the quenched BFMO film. This was attributed to the observed high texturing along (111) orientation. Reduced leakage current density of the quenched BFMO films were explained by defect chemistry with a possibly lower concentration of the oxygen vacancy due to quenching procedure.

Effect of A-site Excess on the Piezoelectric Properties of (K0.48 Na0.52)1+x(Nb0.55Ta0.45)O3 Thin Films

Lead-free polycrystalline (K0.48Na0.52)1+x(Nb0.55Ta0.45)O3 (x = 0, 0.01, 0.02 and 0.03) thin films have been grown on Pt(111)/Ti/SiO2/Si substrates using KrF excimer laser ablation to investigate the effects of A-site ion excess. The film at x = 0.01 exhibited good ferroelectric hysteresis loop with a remnant polarization 2Pr of 30 μC/cm2 and coercive field 2Ec of 61 kV/cm. The piezoelectric coefficient d33,f of the KNNT film with x = 0.01 was found to amount to 79 pm/V. These improved ferroelectric and piezoelectric properties were attributed to the excess of A-site Na and K ions.

Leakage Current Behaviors of SrTiO3 Capped Mn-doped Polycrystalline BiFeO3 Thin Film

The polycrystalline Mn 1% doped BFO (BFMO) thin film was deposited on Pt(111)/Ti/SiO2/Si(100) substrate by pulsed laser deposition. A thin SrTiO3 capping layer was grown on top of deposited Bi(Fe0.99Mn0.01)O3 thin film. The structural and electrical properties of STO/BFMO thin film were investigated. By capping a thin STO on top of BFMO, leakage current density of capacitor was improved greatly compare to that of the pure BFMO without degrading ferroelectricity.