D. Q. Xiao

Preparation and Characterization of (1 — x) Pb(Mg1/3Nb2/3) O3 — x PbTiO3 Electrocaloric Ceramics

Lead magnesium niobate Pb(Mg1/3Nb2/3)O3 — lead titanate PbTiO3 [abbr. as (1 — x) PMN — x PT] ferroelectric ceramics with different excesses of MgO and PbO were systematically studied under different processing conditions for ferroelectric refrigeration application. It was found that the excess amount of MgO and PbO, and the sintering temperature have great effect on the crystallographic properties of the ceramics. In our experiments, (1 — x) PMN —x PT (x = 0.08, x = 0.10, and x = 0.25 respectively) with the excesses of 2 mol% MgO and 2 mol% PbO ceramics sintered at 1250 °C/1 hour possess the desired perovskite structures and large electrocaloric temperature change (ΔT = 1 K and more) in the vicinity of room temperature under a dc electric field of 1.5 kV/mm. It is expected that (1 — x) PMN — x PT electrocaloric ceramics could be applied for cascade refrigeration near room temperature.

Effects of (Li,Ce) on the Dielectric, Piezoelectric and Impendence Properties of CaBi4Ti4O15 Piezoceramics

Aurivillius phase (Li,Ce) doped CaBi4Ti4O15 (CBT) ceramics were prepared using the conventional solid state methods. The crystal structure and microstructure were determined by X-ray diffraction and scanning electron microscopy. It was found that the (Li,Ce) ions diffused into the A site of CBTs pseudo-perovskite structure and formed a single Aurivillius type structure. The Curie-temperature (T C) of CBT based ceramics decreased whereas the piezoelectric coefficient (d 33) was improved with an increase of (Li,Ce) dopants. The detailed electrical properties for Ca0.85(LiCe)0.075Bi4Ti4O15 ceramics in the high temperature region were determined using electrochemical impedance spectra. It was found that oxygen vacancies make a major contribution to both electrical conduction and dielectric relaxation. The ac conductivity was found to obey Jonschers universal law. In addition, the physical nature of electrical conduction and dielectric relaxation was addressed in this paper.

Ferroelectric integrated thin films

Abstract In recent years, great effort has been paid to “Integrated Ferroelectrics”, i.e. the integration of ferroelectric thin films with Si or GaAs chips for developing new devices or systems. Another interesting and potential important area for the investigation of ferroelectric thin films may be the integration of ferroelectric thin films with related functional films, such as piezoelectric and nonlinear optic thin films, for developing multifunctional devices or smart film devices by using the nonlinear or cross-coupling effects based on the interaction of elastic, thermal, electric, magnetic and optical fields in ferroelectric thin films. In this paper, we present some fundamental aspects of ferroelectric integrated thin films from both phenomenological and fabrication points of view, and give some examples of potential devices which can be made from ferroelectric integrated thin films.

Deposition process effect on crystalline structure of (Pb, La) TiO3 thin films by multi – ion – beam reactive cosputtering technique

Abstract Multi—ion—beam reactive cosputtering (MIBRECS) technique is a promising technique for preparing multi—component oxide thin films. However, the deposition processes are critically important for preparing thin films with prospected stoichiometry and good quality. In this paper, the effect of deposition processes, such as substrate temperature, ion beam energy and current, and the postdeposition annealing conditions on the composition and crystalline structure of (Pb, La) TiO3 ferroelectric thin films prepared by MIBRECS technique are reported.

Analyses and syntheses of ferroelectric refrigeration ceramics

Abstract Cryogenic refrigeration could be realized by using the electrocaloric effect (i. e. inverse pyroelectric effect) of ferroelectric materials. Recent progresses implied that ferroelectric refrigeration may be a possible new technique of cryogenic refrigeration operated near room temperature. The analyses and syntheses of ferroelectric refrigeration ceramics of PMN-PT system are presented in this paper

Optical absorption properties of potassium iodate single crystals

Abstract The optical transmissivity of potassium iodate (KIO3) single crystals was measured from ultraviolet to infrared ranges. By using the results in visible range the wavelength dependence of absorption coefficient α and the root of it (α-hν, α1/2-hν) were calculated and the characteristic of absorption edge was discussed. The forbidden energy gap Eg of the crystals, which corresponds to intrinsic absorption related to direct transitions, is 4.13 eV, slightly higher than that in the literature. The absorption edge below 4.13 eV is attributable to indirect transition. The energy gap Eg (3.88 eV) corresponding to indirect transition and the energy Ep (806.7 cm−1) of phonons taking part in indirect transition at room temperature were calculated from α1/2-hν curve, the latter was verified by Raman spectrum of the crystals.

Ferroelectric refrigeration— —A possible new cryogenic refrigeration at room temperature

Cryogenic refrigeration could be realized by using the electrocaloric effect (i. e. inverse pyroelectric effect) of ferroelectric materials. Recent progresses implied that ferroelectric refrigeration may be a possible new technique of cryogenic refrigeration operated near room temperature. The fundamentals, feasibility, present status and the prospect of the research field are briefly introduced in this paper.

Microstructure and impedance analysis of CaBi 4 Ti 4 O 15 piezoceramics with (LiCe)-modifications

(Li, Ce) doped CaBi4Ti4O15 (CBT) ceramics were prepared using the conventional solid state method. The crystal structure and microstructure of CBT-based ceramics were determined by the X-ray diffraction and scanning electron microscopy. It was found that the (Li, Ce) ions diffused into the A site of pseudo-perovskite structure and formed single Aurivillius type structure. The Curie-temperature (TC) of CBT ceramics decreased whereas the piezoelectric coefficient (d33) was improved with the increasing of (Li, Ce) dopants. Furthermore, the impedance spectrum techniques were invoked to understand the electrical properties for pure or modified-CBT compounds at high temperature region and the underlying physical mechanism were also discussed.

In situ deposition of highly C-axis oriented lanthanum modified lead titanate thin films by multi-ion-beam reactive co-sputtering technique

Highly c-axis oriented La-modified PbTiO 3 (PLT) thin films were in situ grown on Pt(100)/MgO(100) and MgO(100) substrates by multi-ion-beam reactive co-sputtering (MIBRECS) technique at the substrate temperature range of 450°C-540°C. The orientation degree α of the films is more than 90%. The chemical composition is in good agreement with the designed one and is almost uniform across the surface of the substrates. The remanent polarization (P r ) and coercive field (E c ) were found to be 5.3 μC/cm 2 and 78 kV/cm, respectively.

Investigation on second-order nonlinear optical polarizations in one-dimensional ionic conductive crystals

Under usual conditions a second-harmonic generation process generates a doubled frequency light which only consists of one polarized state for all nonlinear optical crystals, We found that a doubled frequency light containing two polarized states can be generated under the action of a dc or a low frequency ac field for alpha-LiIO3 and KTiOPO4 crystals. It is considered that the observed phenomenon is attributed to the one-dimensional ionic current.