Jun-Hui He

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.

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 ...

Enhanced room temperature magnetoresistance and cluster spin glass behavior in Mo doping La0.67Sr0.33MnO3

The structural, magnetic, and transport properties of Mo doping La0.67Sr0.33Mn1−xMoxO3 (x=0–0.04) manganite system have been investigated by x-ray diffraction, scanning electron microscopy, magnetization, and magnetoresistance measurements. The Mo doping in Mn site is found to lower the Curie temperature Tc slightly and induce the cluster spin glass behavior in ferromagnetic state of La0.67Sr0.33MnO3. The room temperature magnetoresistance of Mo doping La0.67Sr0.33Mn1−xMoxO3 is found to be 50% higher than that of La0.67Sr0.33MnO3 without Mo doping. The significant enhancement for room temperature magnetoresistance could likely be attributed to the presence of the cluster spin glass state caused by the Mo doping.

PROPERTIES OF Nb-AND Mo-MODIFICATED SrBi4Ti4O15 FERROELECTRIC CERAMICS

ABSTRACT An investigation on the ferroelectric and dielectric properties of higher-valent-cations Nb-and Mo-modificated SrBi4Ti4O15 ceramics was presented. The ferroelectric property of SrBi4Ti4O15 was both obviously improved by niobium and molybdenum doping. The remnant polarization (2P r ) of both Nb-and Mo-modificated SrBi4Ti4O15 increases at first, then decreases with further doping. As the doping content is 0.03 and 0.06 respectively, the 2P r maximizes at a value of 24.7 μC/cm2 and 26.5 μC/cm2, which is about twice larger than that of SrBi4Ti4O15. Meanwhile, the coercive field is increased less than 20% upon Nb and Mo substitution. The Curie temperature of the samples shifted hardly by Nb-and Mo-doping, which indicates that the good thermal stability of SrBi4Ti4O15 is not affected.

SUBSTITUTION SITE OF LANTHANUM IONS IN LA-DOPED SrBi4Ti4O15 and Bi4Ti3O12-SrBi4Ti4O15

ABSTRACT Ferroelectric ceramics of lanthanum-modified SrBi4Ti4O15 and Bi4Ti3O12-SrBi4Ti4O15 have been synthesized, and Raman spectrum measurements have been carried out at room temperature. The investigation on the Raman spectra suggest that La3+ ions prefer to occupy the A site in the case of x ≤ 0.10, and at higher content they tend to be incorporated into Bi2O2 layers in the La-doped SrBi4Ti4O15. As for La-doped Bi4Ti3O12-SrBi4Ti4O15, the critical content of the doping ions is 0.50. An interesting phenomenon has been noticed that the remnant polarization maximized at about the critical doping content. Thus, it can be concluded that the Bi2O2 layers have a very important effect on the properties in the bismuth layer-structured ferroelectric materials.

FERROELECTRIC, PIEZOELECTRIC AND DIELECTRIC PROPERTIES OF Nb MODIFIED Bi4Ti3O12-SrBi4Ti4O15 INTERGROWTH

ABSTRACT Doping and constructing intergrowth are found to be an effectual approach to modify the electrical properties of bismuth layer-structured ferroelectrics. In this work, ferroelectric, piezoelectric and dielectric properties of Nb-doped Bi4Ti3O12-SrBi4Ti4O15 (BTN-SBTN-x) intergrowth ceramics were investigated. The ferroelectric property of Bi4Ti3O12-SrBi4Ti4O15 was improved by niobium doping. The remanent polarization (2P r ) increases at first, then decreases with the increase of niobium content, while the coercive field changes little with Nb-doping. As niobium content is 0.06, the 2P r maximizes at a value of 34.9 μC/cm2, which is increased by about 75% in comparison with that of Bi4Ti3O12-SrBi4Ti4O15 (2P r = 20.0 μC/cm2). The Curie temperature of the samples varies hardly upon Nb-doping, which indicates that the good thermal stability of Bi4Ti3O12-SrBi4Ti4O15 is not deteriorated after Nb addition. Piezoelectric coefficient d33 was increased from 9.3 pC·N−1 to 18.6 pC·N−1 due to the enlargement of 2P r .

EXCELLENT FERROELECTRIC PROPERTIES OF STOICHIOMETRIC AND SR-DEFICIENT Sr2Bi4Ti5O18 THIN FILMS PREPARED BY SOL-GEL PROCESS

ABSTRACT Sr2Bi4Ti5O18 (SBTi) and Sr-deficient SBTi thin films were deposited on Pt/Ti/SiO2/Si(100) substrates using a sol-gel method. Structure, morphology and electric properties were investigated systematically. These films were random-oriented and were composed of rod-like grains. The remanent polarization (2P r ) and coercive field (Ec) of SBTi films were 24 μC/cm2 and 68 kV/cm, respectively. This value of 2P r was much higher than the reported value of SBTi prepared by pulse laser deposition. The compounds with Sr-deficient and Bi-excess composition showed a very large remanent polarization of 35.5 μC/cm2. More importantly, both films showed high fatigue resistance against continuous switching up to 3 × 1010 cycles and excellent charge-retaining ability up to 3 × 104 s.