Papers by Keyword: Lead-Free Ferroelectrics

Abstract: The electro-caloric energy conversions in single-crystal and polycrystalline barium titanate samples are investigated using differential scanning calorimetry (DSC). The DSC measurement reveals a refrigeration effect of 0.1 J/g under an electric field of 15 kV/cm at T=17.5 °C, which is related with the ferroelectric-to-ferroelectric transition in barium titanate. The thermodynamics calculation based on Maxwell’s relations leads to similar conclusion. Such EC effect shows relaxation with the heat release process more significant than the heat adsorption process when the applied field is changed, which is different with those occur near the ferroelectric-to-paraelectric transition temperatures. Furthermore, the electro-caloric energy conversion relation or the scaling relation between the maximum refrigeration effect ΔH and the applied field E, is found to follow a power law ΔH_max~E^b with b=1.72, which is significantly larger than those for EC effects related with the ferroelectric-to-paraelectric transitions.

Abstract: Ferroelectric0.90Bi_0.5Na_0.5TiO₃-0.10BaTiO₃ (0.90BNT-0.10BT) thin film with single perovskite phase is prepared using an improved sol-gel spin coating method onto indium-tin-oxide (ITO) glass substrates. A new solution process is developed for the preparation of precursor solution which is stable in air, presenting a low gelation and trend to the formation of precipitates. The as-prepared thin film is crystallized into single perovskite phase and has good ferroelectric properties. It is remarkable that the thin films show excellent heat-to-electrical energy conversion properties. The results of this work for the first time demonstrate the feasibility of using lead-free BNT-BT films for pyroelectric energy harvesting.

Abstract: Lead-free 0.85(Bi1/2Na1/2)TiO3- 0.10(Bi1/2K1/2)TiO3- 0.05BaTiO3 (BNKB) ceramics with Li2CO3 or (Bi1/2Li1/2)TiO3 (BLT) added were fabricated by a conventional solid oxide route. The XRD analysis indicates that Li2CO3 introduction leads to the increasing of fraction of tetragonal phase while the BLT introduction does in a reverse tendency. Meanwhile, the depolarization temperature Td of Li2CO3-added BNKB ceramics was enhanced obviously while that of BLT-added BNKB ceramics went down as the addition amount increased. The similarity in variation of the phase structure and the Td of BNKB ceramics reveals the nature of Li+ introduction source on phase structure in BNKB ceramics.

Abstract: In this research, it is interesting to fabricate glass ceramics containing lead free ferroelectric crystals. The new lead free ferroelectric phase of interest is orthorhombic Bi2GeO5 which are precipitated in the BiO1.5-GeO2-BO1.5 system and studied in the region of 60 mol% BiO1.5:20 mol% GeO2: 20 mol% BO1.5. The glasses were prepared by conventional melt-quenching method. The glasses were melted separately in Pt and Al2O3 crucible in an air atmosphere. It is found that the as-received glasses were easily obtained from Al2O3 crucible while that from Pt crucible devitrification of Bi2GeO5 crystals were observed in some glasses, giving rise to an instability and difficulty in obtaining good based glasses by using this Pt crucible. The glass ceramics prepared from Pt crucible crystallized into two phases of the expected Bi2GeO5 and second phase Bi4Ge3O12 while Bi2GeO5 phase only observed in the glass ceramics prepared from Al2O3 crucible. Crystallinity and phases of the glass ceramics have a significant effect on their dielectric properties.

Abstract: Phase evolution and physical properties of (1-x)BZT–xBFN ceramic system were investigated to find the optimum condition for electronic applications. (1-x)BZT–xBFN powders were prepared by solid state reaction technique varying x from 0.2 to 0.8 and various sintering temperatures from 1350 °C to 1450 °C. Phase formation was investigated by X-ray diffraction technique. The XRD analysis demonstrated that with increasing BFN content in (1−x)BZT–xBFN, the structural change occurred from the tetragonal to the cubic phase at room temperature. Changes in the physical and mechanical properties were then related to this structural transformation depending on the BFN content.

Abstract: Lead-free Ba(Ti1-xZrx)O3 (BTZ) thin films were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by the chemical solution deposition (CSD) process. The microstructure of the BTZ (x = 0.00 to 0.20) thin films was improved by additional sintering process, and their crystallite sizes were increased in each composition. The dielectric constant er and piezoelectric constant d33 of the BTZ thin films depended on the crystallite size. We give a guide for further investigation to improve the characteristics of BTZ thin films.