Guiyang Shi

Diffused phase transition and multiferroic properties of 0.57(Bi1-xLax)FeO3-0.43PbTiO3 crystalline solutions

Crystalline solutions of 0.57(Bi1−xLax)FeO3−0.43PbTiO3 (BLF-PT) for x=0, 0.1, 0.2, and 0.3 have been fabricated by the solid state reaction method. The dielectric constant of BLF-PT was significantly enhanced by using La substitutions, reaching about 1850 for x=0.3. The ferroelectric-paraelectric phase transition of BLF-PT becomes more diffused with a decreased transition temperature for higher La concentration. BLF-PT of x=0.2 exhibits multiferroic characteristics with the simultaneously enhanced remnant magnetization and polarization of 0.119 emu/g and 33.5 μC/cm2, respectively.

A high temperature piezoelectric ceramic: (1-x)(Bi 0.9 La 0.1 )FeO 3-x PbTiO 3 crystalline solutions

(1-x)(Bi0.9La0.1)FeO3-xPbTiO3 (BLF-PT) crystalline solutions for x = 0.35, 0.37, 0.4, 0.43 and 0.45 have been prepared by the solid-state reaction method. The X-ray diffraction analysis shows that BLF-PT has a single perovskite phase with mixed tetragonal and rhombohedral phases between x = 0.4 and 0.43. The Curie temperature of BLF-PT for x = 0.4 attains 460degC, which is about 80degC higher than that of hard Pb(Zr,Ti)O3 ceramics. The remnant polarization and piezoelectric constant of BLF-PT for x = 0.4 reach 38 muC/cm2 and 112 pC/N, respectively. The planar coupling factor kp of BLF-PT for x = 0.4 remains stable at temperature increases of up to 360degC. The impedance spectroscopy study reveals that the high temperature conduction of BLF-PT may be attributed to the motion of oxygen vacancies within the material. Our results indicate that BLF-PT is a promising candidate for high temperature applications.

Structural and Multiferroic Properties of 1-x(Bi0.85La0.15)FeO3–xPbTiO3 Solid Solutions

A series of solid solutions of 1-x(Bi0.85La0.15)FeO3–xPbTiO3 for x = 0.35, 0.4, 0.415, 0.43, 0.45, 0.47)(BLFPT) are prepared by the mixed oxide method. The X-ray diffraction analysis shows that BLF-PT has a single perovskite phase with mixed tetragonal and rhombohedral phases in x = 0.415. The dielectric constant and Curie temperature of BLF-PT for x = 0.415 is 836 at 102 Hz and 419 °C, respectively. The remnant polarization and magnetization of x = 0.415 reach 39 μC/cm2 and 0.03 emu/g, showing a coexistence of ferroelectricity and ferromagnetism in the vicinity of the morphotropic phase boundary. The structure refinement is used to explain the correlation between structural and multiferroic properties of BLFPT solid solutions, which may be due to the existence of the monoclinic and orthorhombic phases lies on both sides of morphotropic phase boundary.

Piezoelectric properties of low loss and high Curie temperature (Bi, La)FeO3-Pb(Ti, Mn)O3 ceramics with Mn doping

Piezoelectric ceramics of 0.6(Bi0.9La0.1)FeO3-0.4Pb(Ti1−xMnx)O3 (BLF-PTM) for x=0, 0.01, 0.02, and 0.03 were prepared by sol-gel process combined with a solid-state reaction method. The tan δ for BLF-PTM of x=0.01 is just 0.006 at 1 kHz, drastically decreasing by using Mn dopants. The TC increases to 490 °C for BLF-PTM of x=0.02. Furthermore, Mn modification effectively enhances the poling state and the piezoelectric properties of BLF-PTM. The kp, Qm, d33, and g33 of 0.34, 403, and 124 pC·N−1 and 37×10−3 Vm·N−1 are achieved for BLF-PTM of x=0.01. The results indicate that Mn modified BLF-PTM is a competitive high power and high temperature piezoelectric material with excellent piezoelectric properties.

Effects of gallium on the structure and electrical properties of 0.65 Bi 0.94 La 0.06 ) (Ga x Fe 1-x )O 3 -0.35PbTiO 3 ceramics

Crystalline solutions of 0.65 (Bi0.94La0.06) (GaxFe1-x)O3-0.35PbTiO3 ceramics (BLGF-PT) for x = 0 and 0.05 have been fabricated by the solid-state reaction method. X-ray diffraction (XRD) was utilized to characterize the crystal structure and examine any possible impurities existing in the ceramics. The effects of Ga substitution on dielectric properties of the samples were studied at frequencies from 102 to 106 Hz over a temperature range from 20 to 620degC. The results indicate that Ga modification can reduce the room temperature dielectric loss. The conduction mechanism of the material was investigated using ac conductivity. It is concluded that electrons originating from Fe2+ and oxygen ion vacancies are the main charge carriers, and Ga doping could decrease the electronic conduction effectively. The frequency dependence of ac conductivity was found to follow Jonschers universal power law.

Reduced elastic nonlinearity in Mn modified 0.6(Bi0.9La0.1)FeO3–0.4Pb (Ti,Mn)O3 high power piezoceramics

0.6(Bi0.9La0.1)FeO3-0.4Pb(Ti1-xMnx)O-3 (BLF-PTM) piezoelectric ceramics with different Mn contents were fabricated by a sol-gel process combined with a solid-state reaction method. Coexistence of rhombohedral and tetragonal phases is detected in BLF-PTM. An asymmetric P-E loop with a large internal dipolar field of >20 kV cm(-1) is observed in the poled BLF-PTM ceramics of x = 0.01 and 0.02, which is the typical characteristic of hard piezoelectric materials for higher power applications. The dielectric loss, planar coupling coefficient k(p), mechanical quality factor Q(m), vibration velocity, and Curie temperature of 0.006, 0.338, 418, 1.1 m s(-1), and 470 degrees C have been achieved for BLF-PTM with x = 0.01. Furthermore, the elastic nonlinear phenomena in BLF-PTM are investigated by measuring the vibration strain at high electric fields. Upon using Mn doping, BLF-PTM exhibits a large vibration strain and a small resonance frequency shift. The nonlinear elastic compliance of BLF-PTM for x = 0.01 and 0.02 was dramatically decreased by about two orders of magnitude compared to that of BLF-PT for x = 0.

Dielectric and piezoelectric enhancements in the BiFeO 3 -PbTiO 3 solid solutions with Gd doping

Gadolinium doped BiFeO<inf>3</inf>-PbTiO<inf>3</inf> ((Bi<inf>1-x</inf>Gd<inf>x</inf>)FeO<inf>3</inf>-PbTiO<inf>3</inf>, BGF-PT) crystalline solution ceramics for x=0, 0.1, 0.2 and 0.3 are studied in this report. X-ray diffraction (XRD) result reveals that all ceramics are in single perovskite structure. Phase transition from rhombohedral to tetragonal is observed at x=0.1. Enhanced dielectric properties with k=863 and tanδ=0.023 at the frequency of 10² Hz are obtained in BGF-PT of x=0.2. The Curie temperature of BGF-PT for x=0.2 is achieved to 430 °C, which is much higher than La doped BiFeO<inf>3</inf>-PbTiO<inf>3</inf>. Significant piezoelectric enhancements is also found in the BGF-PT ceramics. Our results indicate that BGF-PT is a competitive high temperature piezoelectric material.

Fabrication and characterization of Ti modified BiFeO 3 -PbTiO 3 high temperature piezoelectric ceramics

Solid solutions of 0.65(Bi<inf>0.94</inf>La<inf>0.06</inf>)(Fe<inf>1−x</inf>Ti<inf>x</inf>)O<inf>3</inf>−0.35PbTiO3 (BLFT-PT) for 0.01 ≤ x ≤ 0.06 were fabricated using the mixed oxide method. XRD results indicated that BLFT-PT has a singe perovskite structure and Ti can promote the formation of tetragonal structure. The effects of Ti substitution on dielectric properties of BLFT-PT were studied at frequencies from 10² to 10⁶ Hz over a temperature range from 30 to 650 °C. The results indicate that Ti modification can reduce the room temperature dielectric loss at the low frequencies and increase the dielectric constant of BLFT-PT. The Curie temperature of BLFT-PT for x=0.03 is 525 °C, which is about 140 °C higher than that of PZT ceramics. The impedance spectroscopy study reveals that the high temperature conduction of BLFT-PT may be attributed to the motion of oxygen vacancies within the material. Our results indicate that BLFT-PT is a good candidate high-temperature piezoelectric ceramic with reduced lead content.

Dielectric and multiferroic properties of (Bi,La)FeO 3 -PbTiO 3 ceramics

0.57(Bi<inf>0.8</inf>La<inf>0.2</inf>)FeO<inf>3</inf>-0.43PbTiO<inf>3</inf> (BLF-PT) ceramics were successfully prepared by sol-gel technique combined with solid-state reaction method. X-ray diffraction (XRD) results revealed that single crystallites with rhombohedral phase could be obtained at 600 °C for 2 h, which is 150 °C lower than that required to prepare single phase material with the same composition from solid-state reactions. The average grain size of the powders was ∼60 nm, determined using Transmission electron microscopy (TEM). The analysis of Scanning electron microscopy (SEM) showed that the sintered specimens were dense with the grain size of 2–4 µm. The remanant polarization and magnetization of BLF-PT ceramics were 36 µC/cm² and 0.08 emu/g.

Enhanced dielectric and ferroelectric properties of 0.57(Bi,La)FeO 3 -0.43PbTiO 3 multiferroic ceramics by the Ti substitution

The ceramics of 0.57(Bi<inf>0.8</inf>La<inf>0.2</inf>)(Fe<inf>1x</inf>Ti<inf>x</inf>)O<inf>3</inf>-0.43PbTiO<inf>3</inf> (BLFT-PT) for 0 ≤ x ≤ 0.15 have been synthesized by the solid state reaction method. BLFT-PT ceramics exhibit the dominant rhombohedral structure for x ≤ 0.08, which transfer to the tetragonal phases with further increasing the Ti concentration. However, the second phases are detected for BLFT-PT of x ≥ 0.1. Upon using the Ti substitution, the ac (alternating current) conductivity σ<inf>ac</inf> of BLFT-PT ceramics is significantly reduced at the elevated temperatures. The remnant polarization P<inf>r</inf> and piezoelectric constant d<inf>33</inf> of BLFT-PT are enhanced by the Ti substitution, reaching the maximum of P<inf>r</inf> = 46µC/cm² and d<inf>33</inf> = 262 pC/N for x = 0.05. Our results indicate that BLFT-PT is an alternative multiferroic candidate with excellent piezoelectric properties.