Chaoliang Mao

Doping effects on the electrical conductivity of bismuth layered Bi3TiNbO9-based ceramics

Single phase Bi3TiNbO9 (BTNO)-based ceramics, with Sr2+ replacing Bi3+ as an acceptor dopant and Nb5+ and W6+ replacing Ti4+ as donor dopants, were prepared by conventional solid-state reaction method. The conductivity increased with acceptor dopant and decreased with donor dopant. These results indicate that the dominant conduction mechanism of pure BTNO is p type at low temperature range. Detailed investigations about the W6+ donor doped BTNO ceramics showed that when the doping amount x>0.01, the conductivity increases with increasing donor doping amount, suggesting that the extrinsic conductivity changes from p type to n type at the low temperature region. The extrinsic conductivity range extends to higher temperature with the increase of donor doping amount. At high temperature range the intrinsic electrical conductivity activation energy is about 1.8eV. This value is equal to half the band gap energy.

Poling temperature tuned electric-field-induced ferroelectric to antiferroelectric phase transition in 0.89Bi0.5Na0.5TiO3-0.06BaTiO3-0.05K0.5Na0.5NbO3 ceramics

We report the electric-field-induced ferroelectric (FEIN) to antiferroelectric (AFE) phase transition that is tuned by the poling temperatures in 0.89Bi0.5Na0.5TiO3-0.06BaTiO3-0.05K0.5Na0.5NbO3 (0.89BNT-0.06BT-0.05KNN) ceramics. Phase transition and pyroelectric behaviors of the ceramics were investigated as functions of temperature and electric field. Pyroelectric coefficient peaks of (3 ∼ 6.5) × 10−8 C cm−2 K−1 are detected at about 10 °C above the poling temperatures for the samples poled at different temperatures. The poling temperature tuned pyroelectric behaviors are attributed to the FEIN to AFE phase transition when the temperature increases.

Composition dependence of structural and optical properties for sol-gel derived (100)-oriented Ba1−xSrxTiO3 thin films

Highly (100) oriented Ba1−xSrxTiO3 (BST) thin films were grown on LaNiO3 coated silicon substrate by modified sol-gel process. X-ray diffraction analysis shows that the out-of-plane lattice constant decreases linearly with increase of Sr concentration. The energy band gaps (Eg) of BST thin films exhibit strong dependence on Sr content by analyzing the results of the spectroscopic ellipsometer (SE) measurement. The smallest Eg has been obtained at x=0.3, which is at the phase boundary of cube phase and tetragonal phase. The refractive index and thickness of BST thin films were obtained by fitting SE data with a multiphase model.

Thermal Depolarization and Ferroelectric Properties of (Bi0.5Na0.5)1 - xBaxTiO3 Ceramics

Ferroelectric (Bi 0.5 Na 0.5 ) 1 − x Ba x TiO 3 ceramics with different compositions near the morphotropic phase boundary were fabricated by a citric method. The crystalline structure, microstructure, piezoelectric and ferroelectric properties were systemically studied. A thermal depoling experiment was used to investigate the depolarization temperature and stability of polarization near their depolarization temperature. The results indicated that mix-structured compositions (x = 0.06) have a low depolarization temperature and showed a significant reduction in piezoelectric constant well below their depolarization temperature, while x = 0.08 showed a good resistance to thermal depoling up to their depolarization temperature. The variation trends of the pyroelectric coefficients with different temperature agreed with the thermal depoling experiments and revealed their ferroelectric nature.

Phase characteristics of 0.92Bi0.5Na0.5TiO3-0.08BiAlO3 ceramics

The phase characteristics of 0.92Bi0.5Na0.5TiO3-0.08BiAlO3 lead-free ceramics were investigated systematically. The loss tangent of poled sample shows a broad peak when heating to about 80 °C, i.e., depolarization temperature Td. The polarization-electric field hysteresis loops at different temperature exhibit the feature of ferroelectric (FE)- antiferroelectric (AFE) phase transition and the co-existence of FE and AFE phase. The pyroelectric coefficients curve confirms its diffusion behaviors. The initial hysteresis loop and switching current curves under Td indicate the co-existence of FE and AFE phase. The domain morphology of transmission electron microscopy supports the co-existence of FE and AFE phase. Our work not only exhibit that the FE and AFE phase characteristics of 0.92Bi0.5Na0.5TiO3-0.08BiAlO3 ceramics but also they may be helpful for further investigation on lead-free ceramics.

Dielectric and enhanced pyroelectric properties of (Pb0.325Sr0.675)TiO3 ceramics under direct current bias field

(Pb0.325Sr0.675)TiO3 (PST) ceramics were prepared by a traditional solid-state reaction technique. The dielectric and enhanced pyroelectric properties of PST ceramics were investigated under a DC bias field. The dielectric permittivity and dielectric loss of PST ceramics at Curie temperature were 2.97 × 10−4 and 0.006 without DC bias field, respectively. With a DC electric field of 0–500 V/mm, the maximum pyroelectric coefficient and the largest figure of merit (Fd) of PST ceramics were obtained, about 60 × 10−8 C cm−2 K−1 and 26 × 10−5 Pa−1/2, respectively. PST ceramics with such superior electric field enhanced pyroelectric properties have the potential for uncooled focal plane array detectors application.

Investigation on the Phase Transition Behaviors in Pb0.97La0.02(Zr0.42Sn0.40Ti0.18)O3 Ceramics

Phase transition behaviors in Pb0.97La0.02(Zr0.42Sn0.40Ti0.18)O3 (PLZST) ceramics were investigated by means of polarization, pyroelectric and dielectric studies. The polarization analysis indicated that the initial state of this PLZST ceramics is ferroelectric (FE) and it transforms into a narrow antiferroelectric (AFE) phase when the temperature approaches 120°C. This phase transition behavior was further confirmed by the pyroelectric and dielectric measurements. What is more, after poled, the frequency dispersion in dielectric constant (ϵ) and dissipation factor (tanδ) induced by La modification disappeared.

High temperature dielectric relaxation anomaly of Y3+ and Mn2+ doped barium strontium titanate ceramics

Relaxation like dielectric anomaly is observed in Y3+ and Mn2+ doped barium strontium titanate ceramics when the temperature is over 450 K. Apart from the conventional dielectric relaxation analysis method with Debye or modified Debye equations, which is hard to give exact temperature dependence of the relaxation process, dielectric response in the form of complex impedance, assisted with Cole-Cole impedance model corrected equivalent circuits, is adopted to solve this problem and chase the polarization mechanism in this paper. Through this method, an excellent description to temperature dependence of the dielectric relaxation anomaly and its dominated factors are achieved. Further analysis reveals that the exponential decay of the Cole distribution parameter n with temperature is confirmed to be induced by the microscopic lattice distortion due to ions doping and the interaction between the defects. At last, a clear sight to polarization mechanism containing both the intrinsic dipolar polarization and ex...

Pyroelectric response mechanism of barium strontium titanate ceramics in dielectric bolometer mode: The underlying essence of the enhancing effect of direct current bias field

Pyroelectric response mechanism of Ba0.70Sr0.30TiO3 ceramics under dielectric bolometer (DB) mode was investigated by dielectric and pyroelectric properties measurement. The variations of total, intrinsic, and induced pyroelectric coefficients (ptot, pint, pind) with temperatures and bias fields were analyzed. pint plays the dominant role to ptot through most of the temperature range and pind will be slightly higher than pint above T0. The essence of the enhancing effect of DC bias field on pyroelectric coefficient can be attributed to the high value of pint. This mechanism is useful for the pyroelectric materials (DB mode) applications.

The novel dielectric relaxation behavior around the Curie point of (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics with giant effective permittivity

The temperature (80 K ~ 423 K) and frequency (40 Hz ~ 5 MHz) dependence of the permittivity were studied in (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics. A giant effective permittivity over 105 with a certain frequency and temperature stability and Debye-type dielectric relaxation behavior was observed. The complex impedance spectrum analysis reveals that the giant permittivity is due to the heterogeneous structure with a semiconducting bulk and high resistance electrode–ceramic interface. Deviating from low temperature (below 200 K) thermal activated behavior, the odd change of the characteristic relaxation frequency around the Curie point is observed and proven to be induced by the competition between the positive temperature coefficient of the resistance effect of the bulk ceramic and the dielectric anomaly of the surface layer capacitance, both of which originate from the ferroelectric–paraelectric phase transition.