Xiang-Yu Mao

Properties of lanthanum-doped Bi4Ti3O12–SrBi4Ti4O15 intergrowth ferroelectrics

Lanthanum-doped intergrowth ferroelectrics, (Bi,La)4Ti3O12–Sr(Bi,La)4Ti4O15 [BLT–SBLT(x)], have been prepared. It is found that the remnant polarization (2Pr) of Bi4Ti3O12–SrBi4Ti4O15 (BIT–SBTi) is enlarged. The 2Pr of BLT–SBLT(0.50) has a maximum value of 25.6 μC/cm2. Assuming that the Curie temperature of BLT–SBLT(x) is the average value of the two constituents, La content in both BLT and SBLT can be estimated on the basis of the fact that the crystal structure of BLT–SBLT(x) is not affected by doping. The result shows that when x is not larger than 1.25, La content in BIT is higher than that in SBTi, but when x is 1.50, La content in SBTi is higher. It coincides with the variation of d(118) and the relaxation characteristics of BLT–SBLT(1.50).

Dielectric loss study of oxygen vacancies and domain walls in Sr2Bi4−x/3Ti5−xVxO18 ceramics

An investigation on the ferroelectric and dielectric properties of vanadium-doped Sr2Bi4Ti5O18 ceramics was presented. The ferroelectricity of Sr2Bi4−x/3Ti5−xVxO18 samples (x=0, 0.003, 0.0048, 0.018, 0.048, and 0.096) was obviously improved by vanadium doping. The dielectric property measurement indicated that the Curie temperature was unaffected by vanadium doping, while it displayed a strong dependence of their dielectric loss on vanadium content. One dielectric loss peak around 230 °C related to oxygen vacancies was reduced with doping. Another peak which was just a few degrees below the Curie point and ascribed to viscous motion of domain walls declined drastically with the increase of vanadium content. Those results suggested that the substitution of a small amount of V5+ for Ti4+ reduced the concentration of oxygen vacancies significantly under the restriction of charge neutrality. This led to the weakening of domain pinning and the increasing of the mobility of domain walls, which would be responsi...

Study on properties of lanthanum doped SrBi4Ti4O15 and Sr2Bi4Ti5O18 ferroelectric ceramics

SrBi4-xLaxTi4O15 and Sr2Bi4-xLaxTi5O18 ceramic samples with different lanthanum content, in which x is 0.00, 0.10, 0.25, 0.50, 0.75, 1.00, have been prepared by the solid-state reaction method. It is found that La doping does not change the crystal structures of SrBi4Ti4O15 and Sr2Bi4Ti5O18. Their coercive field (Ec) decreases with the increase of La doping content. The remnant polarization (2Pr) of SrBi4-xLaxTi4O15 increases at first, then decreases with La doping. The 2Pr reaches a maximum value of 24.2 µCcm-2, when x is 0.25. The Ec of SrBi3.75La0.25Ti4O15 is 60.8 kVcm-1. The 2Pr increases by about 50% and the Ec decreases by nearly 25%, compared with those of SrBi4Ti4O15. Obviously, the ferroelectricity of SrBi4Ti4O15 is improved by La doping. The 2Pr and Ec of Sr2Bi4-xLaxTi5O18 decrease monotonically with La doping, and its ferroelectricity is not improved. Their temperatures of phase transition decrease with La doping. The Tc of SrBi3.75La0.25Ti4O15 is 451°C.

Aliovalent B-site modification on three-and four-layer Aurivillius intergrowth

Electrical properties of Nb-, V-, and W-doped Bi4Ti3O12–MBi4Ti4O15 (BIT‐MBTi) (M=Ca,Sr) compounds were investigated. The remanent polarization (2Pr) and piezoelectric coefficient (d33) of BIT‐MBTi are greatly increased by such donor doping. W-doped and Nb-doped BIT-SBTi exhibited the greatest enlargement in 2Pr and d33, respectively. Nb doping also increases 2Pr and d33 of BIT-CBTi though not that much as in the BIT-SBTi case. BIT-CBTi thin film shows a high 2Pr value of 39μC∕cm2. The enhanced properties are thought to stem from the reduced concentration and weakened mobility of oxygen vacancies. Increased activation energy of conduction further confirmed the restraint of oxygen vacancies. The different optimal V-doping content for 2Pr and d33 in BIT-SBTi might be related to the fact that V doping could affect the structure and density of domain more apparently than the concentration of oxygen vacancies. The thermal variation of dielectric constant of BIT-CBTi shows a distinctive double anomaly at 658 and...

Relaxor properties of lanthanum-doped bismuth layer-structured ferroelectrics

Several polycrystalline samples of bismuth layer-structured ferroelectrics (BLSF) family doped by lanthanum, Bi4−xLaxTi3O12, SrBi4−xLaxTi4O15, Sr2Bi4−xLaxTi5O18, and (Bi,La)4Ti3O12‐Sr(Bi,La)4Ti4O15, were prepared by the traditional solid-state reaction method. Their ferroelectric and dielectric properties were investigated. The dielectric measurement data showed that the content of lanthanum determined the ferroelectric characteristics of the compounds. In each series samples, they behaved as normal ferroelectrics for small x, but all of them tended to become relaxors when x was increased. The critical value of the La content causing relaxor characteristics is different for the different BLSFs due to the difference of the number of strontium atoms in their crystal structures. The appearance of the relaxor behavior was attributed to a ferroelectric microdomain state induced by random fields.

Effect of Nd modification on electrical properties of mixed-layer Aurivillius phase Bi4Ti3O12-SrBi4Ti4O15

The effect of Nd modification on ferro-, piezo-, and dielectric properties of intergrowth Bi4Ti3O12-SrBi4Ti4O15 ceramics was investigated. X-ray diffraction and Raman scattering were used to identify the crystal phase and to distinguish the doping sites. With increasing Nd content up to 0.50, both remanent polarization (2Pr) and piezoelectric coefficient (d33) were found to increase and reach the maximum value of 33.2 μC/cm2 and 14 pC/N, respectively, which gained an enlargement over 1.7 times in 2Pr and a desirable 75% increment in d33 value. However, further Nd modification starts to deteriorate the ferro- and piezoelectric behavior. Impedance spectroscopy shows the activation energy of conductivity increased with increasing Nd content, which can be regarded as direct proof of the restraint of oxygen vacancies. The thermal variations of dielectric permittivity and loss tan δ with Nd content show the characteristic of diffuse phase transformation while the convincible defect-related relaxation phenomenon...

Structural and electrical characterization of chemical-solution-derived Bi5FeTi3O15 thin films

Thin films of Fe-containing Aurivillius phase Bi5FeTi3O15 (BFTO) were prepared using the chemical solution deposition method. The structures of the films were analysed using x-ray diffraction and Raman spectroscopy. The surface topography and crystal microstructure were characterized by AFM and FESEM. The remanent polarization (2Pr) and coercive field (Ec) of BFTO thin films under an electric field of ~570 kV cm−1 are determined to be 35.5 µC cm−2 and 171 kV cm−1, respectively. The normalized polarization of BFTO thin films under 285 kV cm−1 decreased to 66% after being subjected to 5.2 × 109 read/write cycles. A comparison between BFTO and SrBi4Ti4O15 in Raman spectra and ferroelectric behaviour is also presented. The leakage current density measurement reveals that the conduction mechanism of BFTO thin films in the intermediate electric field range from ~50 to ~200 kV cm−1 is dominated by Schottky emission. With an electric field higher than ~200 kV cm−1, the leakage behaviour is mingled with different conduction mechanisms.

Ferroelectric and dielectric properties of niobium-doped SrBi4Ti4O15 ceramics

An investigation of the ferroelectric and dielectric properties of niobium-doped SrBi4Ti4O15 (SrBi4−x/3Ti4−xNbxO15, x = 0.00, 0.003, 0.012, 0.03, 0.06) ceramics was presented. The ferroelectric property of SrBi4Ti4O15 was improved by niobium doping. The remanent polarization (2Pr) increases at first, then decreases with the increase in niobium content, while the coercive field changes little with Nb-doping. As the niobium content is 0.03, the 2Pr maximizes at a value of 24.7 µC cm−2, which is increased by about 60% in comparison with that of SrBi4Ti4O15. The Curie temperature of the samples hardly varies upon Nb-doping, which indicates that the good thermal stability of SrBi4Ti4O15 does not deteriorate after Nb addition.

Properties of nd-substituted SrBi4Ti4O15 ferroelectric ceramics

Ceramic samples of SrBi4−xNdxTi4O15 (SBNT-x, x = 0.00–1.00) have been prepared by the conventional solid-state reaction method. As the Nd doping content increases from 0.00 to 0.18, the remnant polarization (2Pr) increases steadily and reaches a maximum value of 25.8 µC cm−2, which is almost 56% higher than that of the non-doped sample. However, 2Pr decreases with further substitution. The variation of 2Pr is dominated by the restraint of space charge and the relief of structural distortion. The coercive field (Ec) remains almost unchanged at a value of ~80 kV cm−1 in the case of x = 0.00–0.18, then decreases with further Nd-doping, which is probably due to the formation of anti-phase boundaries induced by the modification. As doping content exceeds 0.75, the specimens exhibit relaxor behaviour due to a ferroelectric microdomain state caused by the random fields.

Structural, ferroelectric, and dielectric properties of vanadium-doped Bi4-x/3Ti3-xVxO12

The microstructure, ferroelectric, and dielectric properties of vanadium-doped Bi4Ti3O12 ceramics have been investigated. V substitution is found to cause a transition from an orthorhombic phase to a tetragonal phase at x∼0.03, and again to an orthorhombic phase at higher V content. The ferroelectric properties of Bi4Ti3O12 were significantly improved by V doping. The 2Pr of Bi4Ti3O12 is 16μC∕cm2, and it reaches a maximum value of 26.4μC∕cm2 when the V content is 0.03. The two relaxation peaks (PI, PII) are observed in the dielectric loss (D) curves for all of the samples. The PI and PII peaks related to oxygen vacancies tend to decrease with V doping, which implies the decreasing of the oxygen vacancy concentration caused by V doping and favors the improvement of 2Pr and 2Ec. On the contrary, Raman spectra reveal the occurrence of Ti vacancies when V content is more than x=0.01, which may be responsible for the variation of the microstructure and the deterioration of 2Pr and 2Ec. The ferroelectricity of ...