Influences of ScTa cosubstitution on the properti

Authors: ZhiGang Gai MingLei Zhao WenBin Su ChunLei Wang Jian Liu JiaLiang Zhang

Publish Date: 2013/06/15

Volume: 31, Issue: 1-2, Pages: 143-147

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Abstract

The effect of ScTa doping on the properties of Bi3TiNbO9based ceramics was investigated The ScTa modification greatly improves the piezoelectric activity of Bi3TiNbO9based ceramics and significantly decreases the dielectric dissipation The d33 of Bi3Ti096Sc002Ta002NbO9 was found to be 12 pC/N the highest value among the Bi3TiNbO9based ceramics and almost 2 times as much as the reported d33 values of the pure BTNO ceramics ~6pC/N The high TC higher than 900 °C and stable piezoelectric and dielectric properties demonstrating that the ScTa modified Bi3Ti1−xScx/2Tax/2NbO9based material a candidate for ultrahigh temperature applications The new ScTa modification has an important typical significance the way should be used for reference in constructing the new high performance materialsBismuth layerstructured ferroelectrics BLSFs ceramics are potential candidate leadfree materials in piezoelectric device application especially at high temperatures and high frequencies application In addition to their high Curie temperatures they exhibit correspondingly low temperature coefficients of dielectric and piezoelectric properties low aging rate strong anisotropic electromechanical coupling factors and low temperature coefficient of resonant frequency making them suitable for pressure sensors trapped energy filters etc 1 2In recent years BLSFs have been given more attention BLSFs such as SrBi2Na2O9 SBN SrBi4Ti4O15 SBTi SrBi2Ta2O9 SBT La075Bi325Ti3O12 BLT etc have been found to be excellent materials for nonvolatile ferroelectric random access memory FRAM owing to their fatigue free polarization behavior 3 4 5 6 7 The general formula of BLSF is Bi2O22+Am−1BmO3m+12− where A is a mono di or trivalent element or a combination of them allowing dodecahedral coordination and B is a transition element with octahedral coordination eg Ti4+ Nb5+ Fe3+ W6+ or Ta5+ m is the number of octahedral layers in the perovskite slab which varies from 1 to 6 4 8 The poling of the BLSF ceramics requires relatively high electric field because of their high coercive fields and the twodimensional orientation restriction of rotation of the spontaneous polarizationBismuth titanate niobate Bi3TiNbO9 hereinafter called BTNO m = 2 which is made up of Bi2O22+ layers between which BiTiNbO72− layers are inserted 9 is promising for high temperature piezoelectric sensors because of its very high Tc 914 °C 8 However the piezoactivity of pure BTNO ceramics is quite low d 33  7 pC/N 10 for high temperature applications The Asite substitution or/and Bsite substitution have been shown to be effective in modifying the structure and polarization process 11 12 13 14 15 16 17 18 19 20 21 22 23 Only a few works have addressed the properties of cationmodified BTNObased ceramics For La and Ti/Wsubstituted BTNO24 and Bi2K1/6Bi5/6TiNb2/3W1/3O9 25 compounds only a few properties eg lattice parameters and Tc have been mentioned and no detailed structural and electrical properties have been studied To modify BTNO structure for improving its piezoelectricity the ScTa cosubstitution into Bsite of BTNO was conductedThe only valence of Sc is 3 and the only valence of Ta is 5 so the average valence of ScTa is 4 which is equal to the only valence of Ti4+ The radius of Sc3+ is 0073 nm and the radius of Ta5+ is 0068 nm They are almost the same as the radius of Ti4+ r Ti 4+ =0068 nm More than that Sc Ta Ti and Nb in the BLSF structure have the same favorable coordinate number which is 6 All of those can assure the Sc3+Ta5+ cosubstitute Ti4+ into Bsite of BTNO Because the valence of Nb is 5 which is different from the average valence of ScTa and the law of conservation of electric the ScTa will not cosubstitute Nb In addition the samples will be prepared according the formula Bi3Ti1−xScTax/2NbO9 so there is not lack of Nb which will lead Nb to stay at the original position without being substituted The starting raw materials were high purity Bi2O3 998  TiO2 998  Nb2O5 995  Sc2O3 9927  Ta2O5995  The samples were prepared according the formula Bi3Ti1−xScTax/2NbO9 x = 000 002 004 006 The chemicals were weighed according to the composition and then mixed using ball milling dried and calcined at 808 °C for 3 h After calcination the ballmilled ground powders were pressed into disks with 13 mm in diameter and 2 mm in thickness Densification was achieved by sintering the disks at 1080 °C for 2 h in a sealed crucible to prevent volatilizationThe Xray diffraction XRD patterns for the ceramic powers were obtained with an Xray diffractometer PGeneral XD3 patterns using Cu Kα radiation For room temperature electrical and dielectric properties measurement platinum electrodes 1 cm2 are fixed on both surfaces of the sintered pellets and fired at 800 °C for 20 min in air Samples were poled in silicone oil at 200 °C under a dc electric field from 100 kV to 150 kV/cm for 60–120 min The piezoelectric coefficient d 33 was measured using a quasistatic d 33 meter Institute of Acoustics Academia Sinica ZJ2 The temperature dependence of the resistivity ρ was determined using a high resistance meter Shanghai ZC43 with an applied voltage of 20 Volts The planar coupling k p and the thickness coupling k t were determined by the resonanceantiresonance method by using an Impedance Analyzer Agilent 4294A The dielectric behavior was also measured using an Impedance Analyzer Agilent 4294A at 1000 kHz as a function of temperature

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