PbZr0.52Ti0.48O3 thin films on stainless steel substrates were fabricated by an ethylene glycol modified sol–gel method. Perovskite structure of PbZr0.52Ti0.48O3 thin films was examined by the X-ray diffraction analysis. With the increase of ethylene glycol, PbZr0.52Ti0.48O3 thin films with enhanced dielectric and ferroelectric properties were got. Crack-free PbZr0.52Ti0.48O3 thin films with thickness of 1.6 μm were prepared for ethylene glycol content of 50%, and the dielectric permittivity and dielectric loss were 224 and 5.4% respectively at the frequency of 1 kHz showing better dielectric properties compared with PbZr0.52Ti0.48O3 thin films without ethylene glycol modified. The remnant polarization (Pr) of 50% content ethylene glycol modified PbZr0.52Ti0.48O3 thin films was nearly twice reaching 12.3 μC/cm2, and lower leakage current density was obtained with 4.6 × 10−6 A· cm−2 under the field of 50 kV· cm−1. Such enhanced performance indicated that the PbZr0.52Ti0.48O3 thin films prepared on stainless steel substrates by the ethylene glycol modified sol–gel process exhibited their potentiality in applications.Open image in new window

•PZT/BST multilayer thin films on Ti substrates were fabricated by sol-gel method.•The maximum tunability reaches 41.1% under 400 kV/cm when the content of BST is 50%.•Dielectric temperature stability is enhanced and leakage current density is reduced.•From phenomenological theory, electrostatic coupling takes place in fabricated films.PbZr0.2Ti0.8O3/Ba0.6Sr0.4TiO3 (PZT/BST) multilayer thin films on LaNiO3 buffered Ti substrates were fabricated by sol-gel method. Results show that there are tetragonal PZT phase and cubic BST phase in the phase structure of PZT/BST films. These films with small grain size also exhibit enhanced dielectric temperature stability and reduced leakage current density. Dielectric anomaly is found for such PZT/BST multilayers: the maximum of dielectric constant and tunability respectively reaches 501 and 41.1% (400 kV/cm) when the thickness content of BST films is 50%. The corresponding temperature coefficient of permittivity (TCP) is only 2.7 × 10−4/°C. Furthermore, dielectric constant and tunability of such PZT/BST thin films are calculated by phenomenological theory. The experimental data of dielectric constant and tunability are both in between the calculated results of without and complete electrostatic coupling, indicating that dielectric anomaly is caused by electrostatic coupling and part coupling takes place in the fabricated films.

Barium strontium titanate (BST) thin films deposited on stainless steel (SS) substrates can be expected for their potential applications in MEMS-structure tunable microwave devices. In this paper, two sandwich-like structures with varied average Ba/Sr ratio of BST thin films, Ba0.6Sr0.4TiO3 layer in the middle or at ends, on LaNiO3 buffered SS substrates were fabricated by sol–gel technique, and meanwhile were theoretically carried out via a modified phenomenological model. Results show that dielectric constant and tunability of such BST films can be tailored by average Ba/Sr ratio and structures. When the average Ba/Sr ratio is unchanged, the structure with smaller lattice parameter of middle layer than that of top/bottom layer can achieve larger tunability resulting from its smaller compressive misfit strain, which has been qualitatively characterized by X-ray diffraction and Raman spectra. Especially, the largest tunability reaches 30 % under the electric field of 300 kV cm−1 by locating Ba0.4Sr0.6TiO3 layer in the middle and Ba0.6Sr0.4TiO3 layers at ends. Furthermore, the experimental dielectric constants and tunabilities are in good agreement with the calculated data, instructing that the dielectric properties of BST thin films with unchanged Ba/Sr ratio can be tailored by changing the structure to adjust the lattice misfit strain of each uniform layer. This implies that multilayer BST thin films also can be designed by phenomenological theory.

Bismuth ferrite crystallites were prepared by the hydrothermal method. The phase evolution in the process of hydrothermal reactions was investigated for different conditions. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicates that sillenite Bi25FeO40 could be the intermediate products, while perovskite BiFeO3 was the target crystallite. The phase evolution could be controlled by adjusting KOH concentration, reaction temperature and duration time et al. The dissolution of Fe(OH)3 plays an important role to control the phase formation of bismuth ferrites. Bi25FeO40 and BiFeO3 crystallites have the cubic and sphere-like morphologies respectively. The formation of perovskite BiFeO3 crystallites was based on the dissolution of sillenite Bi25FeO40.Highlights► Sillenite Bi25FeO40 is the intermediate phase in the formation of pervoskite BiFeO3. ► Phase evolution can be controlled by adjusting the process parameters. ► The dissolution of Fe(OH)3 plays an important role to control the phase evolution of bismuth ferrites. ► The formation of perovskite BiFeO3 crystallites was based on the dissolution of sillenite Bi25FeO40.

PbZr0.53Ti0.47O3 (PZT) ferroelectric thin films were deposited on LaNiO3 (LNO) by sol-gel method. The PbTiO3 (PT) seed layer was deposited between the LNO buffer layer and stainless steel (SS) substrate, which effectively decreased the annealing temperature of LNO layer from 750 °C to 650 °C. X-ray diffraction (XRD) reveals that LNO layers with PT layer crystallize into a perovskite phase on annealing at 650 °C for 10 min. PZT deposited on LNO buffer layer with PT seed layer exhibits good ferroelectric property.

Piezoelectric ceramics of 0.6(Bi0.9La0.1)FeO3-0.4Pb(Ti1−xMnx)O3 (BLF-PTM) for x=0, 0.01, 0.02, and 0.03 were prepared by sol-gel process combined with a solid-state reaction method. The tan δ for BLF-PTM of x=0.01 is just 0.006 at 1 kHz, drastically decreasing by using Mn dopants. The TC increases to 490 °C for BLF-PTM of x=0.02. Furthermore, Mn modification effectively enhances the poling state and the piezoelectric properties of BLF-PTM. The kp, Qm, d33, and g33 of 0.34, 403, and 124 pC·N−1 and 37×10−3 Vm·N−1 are achieved for BLF-PTM of x=0.01. The results indicate that Mn modified BLF-PTM is a competitive high power and high temperature piezoelectric material with excellent piezoelectric properties.

Pb(Zr0.53Ti0.47)O3 (PZT) thin films were prepared on La0.5Sr0.5CoO3 (LSCO) coated Si substrates by a sol–gel route. The thickness of LSCO electrode was found to modify the preferential orientation of PZT thin films, which consequently affected the dielectric and ferroelectric properties. (100) textured PZT films with dense columnar structure could be obtained on the top of (110) textured LSCO with thickness of 230 nm. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm2, respectively.

Ba0.6Sr0.4TiO3 (BST) thin films with and without HfO2 buffer layer were fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition. Dependences of HfO2 thickness on the dielectric property and leakage current of BST thin films were focused. The dielectric constant of BST thin films increased and then decreased with the increase of HfO2 thickness, while the dielectric relaxation was gradually improved. The loss tangent and leakage current under positive bias decreased with the HfO2 thickness increasing. The leakage current analysis based on the Schottky emission indicated an improvement of the BST/Pt interface with HfO2 buffer layer. The loss tangent, tunability and figure of merit of optimized HfO2 buffered BST thin film achieved 0.009 8, 21.91% (Emax= 200 kV/cm), 22.40 at 106 Hz, respectively.

Sol-gel derived Pb(Zr0.53Ti0.47)O3 (PZT) thin films were prepared on LaNiO3 (LNO) buffered titanium foils. The effect of LNO buffer layer thickness on the electric properties of PZT thin films was investigated. The room temperature dielectric constant of PZT thin films increased with increasing LNO thickness. The remnant polarization of PZT thin films on 150 and 250 nm LNO was about 20 uC/cm2. Curie temperatures of PZT thin films were 310, 330 and 340 °C for LNO of 250, 150 and 50 nm respectively. The current-voltage characteristics of PZT thin films were examined for different LNO buffer layer thicknesses, and the space charge limited conduction model was followed in PZT thin films on 50 nm LNO.

Oriented growth of Bi2Fe4O9 crystals were synthesized by a facile hydrothermal route in the presence of different organic additives. X-ray diffraction was used to characterize the derived powders, indicating that single-phase Bi2Fe4O9 with growth orientation along the (001) and (221) planes were obtained respectively. Extensive structural characterization of the as-prepared samples was observed using Fourier transform infrared spectroscopy, Scanning electron microscope, and UV-vis diffuse reflectance spectrum. The photocatalytic activity of Bi2Fe4O9 powders with different orientation was evaluated on degradation of methyl orange solution under visible light irradiation. The results show that the photocatalytic activity of the (001) plane is much higher than that of the (221) plane.