Effects of Microstructure and Electrical Properties of Strontium and Manganese-Doped (1-x)(Bi0.5Na0.5)TiO3 -(x)BaTiO3 Piezoelectric Ceramics

• Main Authors: LEE, YI-TSUNG, 李奕璁
• Other Authors: CHEN, PIN-YI
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/83717488707369979781

碩士 === 明志科技大學 === 機械工程系機械與機電工程碩士班 === 105 === This study reports the piezoelectric properties of lead-free (Bi0.5Na0.5)(0.925-x)Ba0.075SrxTiO3 ceramics (BNT-7.5BT-x%ST, 0 ≤ x ≤ 0.30) and (Bi0.5Na0.5)0.725Ba0.075Sr0.2Ti(1-y)MnyO3 (BNT-7.5BT-20%ST-y%Mn, 0 ≤ y ≤ 0.02) ceramics fabricated by solid state reaction method. The A-site of strontium (Sr) substitution for bismuth (Bi) and sodium (Na) and the B-site of manganese (Mn) substitution for titanium (Ti), not only increased dielectric permittivity, but also enhanced the relaxor behavior and piezoelectric properties. X-ray diffraction (XRD) measurement and TEM investigation were car-ried out to identify phase and structural characteristics. Experimental results show that BNT-7.5BT-x%ST ceramics will transit to pseudo-cubic structure (Pm3m + P4bm) as Sr doping content reached to 25%, which is different from pure BNT-7.5BT ceramics with rhombohedral R3c and tetragonal P4bm phases. The suitable strontium doping can enhance the direct piezoelectric coefficient d33 reaches a maximum d33 of 190 pC/N. P–E hysteresis loop measurements exhibit a phase transition from ferroelectric to relaxor ferroelectric states by doping above 25mol%Sr in BNT-7.5BT-xST ceramics. The E-field induced strain can reach to a maximum value of 0.23% in 30mol%Sr-doped BNT-7.5BT ceramic. The temperature-independent dielectric permittivity (ε') measurements show that Sr doping can lower depolarization temperature Td from the 130℃ to room temperature, and improve structural thermal stability for BNT-7.5BT-x%ST ceramics. For BNT-7.5BT-20%ST-y%Mn ceramics, with the increase of the mole ra-tio (y) of manganese, the phase structure is gradually changed to pseudo-cubic phase with major P4bm symmetry. XAS experiments indicate that the elec-tronic orbital hybridization between O 2p and Mn 3d is decreased with in-creasing the manganese content, which implying the Mn doping may play a weakening Mn-O bonding role. Moreover, XAS of Mn L-edge reveal a mixture of Mn2+, Mn3+, and Mn4+ valence states in BNT-7.5BT-20%ST-y%Mn ceramics. The results suggest that parts of Mn ionic valence transit from original Mn4+ toward Mn2+ and Mn3+, which leads to the formation of oxygen vacancies and grain growth in the sintering period simultaneously, especially, as Mn doping content above 1mol%. Temperature-depentent dielectric permittivity measurements show that both of the maximum temperature Tm and the Burn temperature TB of dielectric permittivity move to high temperature, and the dielectric constant at room temperature decreases gradually as well as the phenomenon of frequency dispersion is less obvious with increasing the amount of Mn. These results are attributed to the enhanced P4bm phase and abumdent oxygen vacancies can stabilize local polarization by the Mn doping.