Key Engineering Materials Vols. 368-372

Abstract: Ba0.5Sr0.5TiO3 (BSTO) ceramics were synthesized by spark plasma sintering (SPS) technique. The phase compositions, microstructure and dielectric properties of BSTO ceramics were investigated. The results indicated that SPS was an alternative sintering technology to synthesize dense BSTO ferroelectric ceramics at low temperature and in a short period.

Abstract: (1-X)BaTiO3-XCaCu2.94Mn0.06Ti4O12 (BTO-CCMTO) composite ceramics with X =0.1 and 0.2 were prepared through solid state reaction route. X-ray diffraction (XRD) analyses showed that a co-existence structure of BTO and CCMTO phase can be realized when the sample was sintered at 950°C. Furthermore, influences of CCMTO on the dielectric behaviors of the BTO-CCMTO composite ceramics were investigated. The results showed that the dielectric permittivity of the BTO-CCMTO composite ceramics increases with increasing amounts of CCMTO and the Curie peak of the pure BTO ceramics is greatly suppressed due to the addition of CCMTO. The dielectric loss of the BTO-CCMTO composite ceramics can be kept in the same magnitude order as that of the BTO ceramics.

Abstract: In this study, piezoelectric materials 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 (NBT-BT) composition with excess x wt% Bi2O3 (x=0, 1, 2, and 3) are investigated as a function of sintering temperatures. The sintering characteristics and dielectric characteristics of excess Bi2O3-doped 0.95 (Na0.5Bi0.5)TiO3- 0.05 BaTiO3 ceramics are developed with the aid of SEM, XRD patterns, and dielectric-temperature curves. The sintering process is carried out in air for 2h from 1120oC to 1200oC. Dielectric-temperature properties are investigated in the temperature range of 30oC~350oC at the frequencies of 10KHz~1MHz. The maximum dielectric constants of NBT-BT ceramics first increase with the increase of Bi2O3 content, reach the maximum at 1wt%- Bi2O3-added NBT-BT ceramics, and then decrease with the further increase of Bi2O3 content. The maximum dielectric constants of NBT-BT ceramics are almost unchanged as the measured frequency increases. The Curie temperatures of NBT-BT ceramics are also developed.

Abstract: Lead-free piezoelectric ceramics of (Na0.8K0.2)0.5Bi0.5TiO3+x wt.% Mn (abbreviated as NBKT-x% Mn, x=0~0.5) were synthesized by solid-state reaction. The grain growth of the ceramics was restrained by Mn-doping at a certain extent. The mechanical quality factor Qm increases and the dielectric loss tanδ decreases with the increase of Mn-doping. Best piezoelectric properties were obtained for the composition of NKBT-0.2%Mn: d33=158 pC·N-1, tanδ=2.9% at 1 kHz, Qm=110 and kp=30%. The P-E loops show that remnant polarization Pr and coercive field Ec decrease slightly with the amount of the Mn2+ increasing up to 0.2wt.% and then increase as the content of Mn2+ increases further. NKBT-0.5wt. % Mn exhibits strong ferroelectricity with remnant polarization Pr = 38μC/cm2.

Abstract: The effects of Mn doping on the phase composition and dielectric properties of (1-x)BaO·xSrO·0.7TiO2·0.3Nb2O5 (BSTN) composite ceramics was investigated. The results showed that the dielectric constants of 0.7BaO·0.3SrO·(0.7-z)TiO2·0.3Nb2O5·zMnO2 (BSTNM) composite ceramics basically decreases as the content of doped MnO2 increases at the same applied frequency, while tanδ decreases when value z≤0.01 but increases when value z>0.01. The phase transition temperature of tungsten bronze phase in BSTNM composite ceramics increases with the increase of value z.

Abstract: In this study, the effects of oxygen gas plasma on the surface treatment of Ba(Zr0.1Ti0.9)O3 (BZT) films are investigated. The influence of plasma on the structure is developed by using X-ray diffraction patterns and the electrical characteristics are developed by using the MIM and MFIS capacitor structure. Experiment results clearly indicate that the electrical characteristics of BZT film have improved effectively within oxygen plasma surface treatment.

Abstract: Bi-doped Sr0.7Ba0.3TiO3 ceramics sintered at different temperatures were studied by analytical electron microscopy. Grain boundaries (GBs) with discrete Bi nano-precipitates (NP) were observed in both samples sintered at 1170°C and 1190°C. Dopants’ solutions as well as their segregations to GB were analyzed quantitatively to reveal the origin of NP. NP at GB contributed to the high dielectric constants of the materials.

Abstract: Tb-doped bismuth titanate (BixTbyTi3O12: BTT) and pure Bi4Ti3O12 (BIT) thin films with random orientation were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well-developed rod-like grains with random orientation. Tb doping into BIT caused a large shift of the Curie temperature (TC) from 675°C to lower temperature. The experimental results indicated that Tb doping into BIT result in a remarkable improvement in dielectric property.

Abstract: Pr-doped bismuth titanate (BixPryTi3O12: BPT) thin films with random orientation were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the structures and Raman spectra of the films were investigated. XRD studies indicated that all of the BPT films consist of single phase of a bismuth-layered structure, showing a highly (117) oriented preferential growth with a minor fraction of (00l) orientation. For an increasing degree of Pr doping, Raman spectra studies revealed a substantial hardening of the vibration involving Bi atoms at the perovskite A site, whereas the Bi mode at the Bi2O2 layer is negligibly changed. From a comparison with a simple mass consideration, we identify a precise cation distribution, indicating a pronounced site selectivity of Pr ions for the A site for y ~ 1.2.

Abstract: The electrical properties of Bi3.25Dy0.75Ti3O12 (BDT) and Bi3.25Gd0.75Ti3O12 (BGT) ceramics were investigated. The current-voltage curve of the BGT sample exhibits a negative differential resistance behavior, whereas that of the BDT sample exhibits a simple ohmic behavior. The impedance spectrum of the BDT and BGT samples indicate that both consist of semiconducting grain and moderately insulating grain boundary regions. XRD, SEM and EPMA analyses reveal crystalline phase characterized by a Bi-layered perovskite structure of Bi4Ti3O12 and the distribution of every element is uniform. Both BDT and BGT samples exhibit randomly oriented and plate-like morphology.