Structural,dielectric and piezoelectric properties of (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–Bi(Zn0.5Ti0.5)O3 thin films prepared by sol–gel method

Lead free (1−x)(0.8Bi_0.5Na_0.5Ti_0.5O₃–0.2Bi_0.5K_0.5TiO₃)–xBiZn_0.5Ti_0.5O₃ (x=0–0.06) (BNT–BKT–BZT) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel processing technique. The effects of BZT content on the structural, dielectric, ferroelectric and piezoelectric properties of the BNT–BKT–BZT thin films were investigated systematically. The BNT–BKT–BZT thin films undergo a transition from ferroelectric to relaxor phase with increasing temperature. The phase transition temperature decreases with the increase of BZT content. The BNT–BKT–BZT thin film with x=0.04 exhibits the best ferroelectric properties (P_max=40 µC/cm² and P_r=10 µC/cm²), largest dielectric constant (ε=560) and piezoelectric constant (d₃₃=40 pm/V). This finding demonstrates that the BNT–BKT–BZT thin film has an excellent potential for demanding high piezoelectric properties in lead free films.     

Ferroelectric and dielectric properties of manganese-doped Na0.5Bi0.5TiO3 nanocrystalline thin films prepared by metal organic decomposition: A single-layer thickness-dependent study

2 at% Manganese-doped Na_0.5Bi_0.5TiO₃ (NBTMn) thin films with single-layer thicknesses ranging from 15 to 45 nm/l were deposited on the indium tin oxide/glass substrates by a metal organic decomposition process and spin coating technique. The influence of single-layer thickness on the crystal structure, surface morphology, insulating ability, ferroelectric and dielectric properties was mainly investigated. Compared with the other films, NBTMn film with a single-layer thickness of 30 nm/l exhibits the (110)-preferred orientation and dense structure. Also, it shows the enhanced ferroelectricity with a large remanent polarization (P_r) of 38 μC/cm² due to the preferred orientation and low leakage current density. Meanwhile, a high dielectric tunability of 39% for NBTMn with 30 nm/l can be observed by varying the measuring applied voltage and frequency. These results indicate that the suitable layer thickness is beneficial to improve the electrical performances of NBTMn thin film.     

Synthesis and electrical properties of lead-free piezoelectric Bi0.5Na0.5TiO3 thin films prepared by Sol-Gel method

Lead-free Bi_0.5Na_0.5TiO₃ (BNT) piezoelectric thin films were deposited on Pt/TiO_x/SiO₂/Si substrates by Sol-Gel method. A dense and well crystallized thin film with a perovskite phase was obtained by annealing the film at 700 °C in a rapid thermal processing system. The relative dielectric constant and loss tangent at 12 kHz, of BNT thin film with 350 nm thickness, were 425 and 0.07, respectively. Ferroelectric hysteresis measurements indicated a remnant polarization value of 9 μC/cm² and a coercive field of 90 kV/cm. Piezoelectric measurements at the macroscopic level were also performed: a piezoelectric coefficient (d_33effmax) of 47 pm/V at E = 190 kV/cm was obtained. The piezoresponse force microscopy data confirmed that BNT thin films present ferroelectric and piezoelectric behavior at the nanoscale level.     

Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films

Lead free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ thin films doped with BiFeO₃ (abbreviated as BNKT-xBFO) (x = 0, 0.02, 0.04, 0.08, 0.10) were deposited on Pt(111)/Ti/SiO₂/Si substrates by sol-gel/spin coating technique and the effects of BiFeO₃ content on the crystal structure and electrical properties were investigated in detail. The results showed that all the BNKT-xBFO thin films exhibited a single perovskite phase structure and high-dense surface. Reduced leakage current density, enhanced dielectric and ferroelectric properties were achieved at the optimal composition of BNKT-0.10BFO thin films, with a leakage current density, dielectric constant, dielectric loss and maximum polarization of < 2 × 10⁻⁴ A/cm³, ~ 978^, ~ 0.028 and ~ 74.13 μC/cm² at room temperature, respectively. Moreover, the BNKT-0.10BFO thin films possessed superior energy storage properties due to their slim P-E loops and large maximum polarization, with an energy storage density of 22.12 J/cm³ and an energy conversion efficiency of 60.85% under a relatively low electric field of 1200 kV/cm. Furthermore, the first half period of the BNKT-0.10BFO thin film capacitor was about 0.15 μs, during which most charges and energy were released. The large recoverable energy density and the fast discharge process indicated the potential application of the BNKT-0.10BFO thin films in electrostatic capacitors and embedded devices.     

Thickness dependent growth and ferroelectric/dielectric properties of phase-pure 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 thin film derived from a modified sol-gel process

Annealing parameter and thickness are two significant factors affecting microstructure and electrical performance of sol-gel derived 0.65Pb(Mg_1/3Nb_2/3)O₃?0.35PbTiO₃ (0.65PMN-0.35PT) thin film. In this paper, various durations are firstly selected for the investigations on annealing parameter of 0.65PMN-0.35PT thin film. Enhanced insulating and ferroelectric properties can be obtained for the film annealed for 1 min due to its phase-pure and homogeneous perovskite structure. Based on this, a series of 0.65PMN-0.35PT thin films with various thicknesses by modifying deposition layer are synthesized annealed for 1 min and the effects of thickness on crystalline, insulating, ferroelectric and dielectric properties are characterized. It reveals that thickness-dependent behavior can be noticed for 0.65PMN-0.35PT thin film with the results that the 8-layered film possesses a relative large remanent polarization (P_r) of 23.34 μC/cm², and reduced leakage current density of 10^?9 A/cm² with low dissipation factor (tanδ) of 0.03 can be achieved for the 14-layered film.     

The microstructure,ferroelectric and dielectric behaviors of Na0.5Bi0.5(Ti,Fe)O3 thin films synthesized by chemical solution deposition: Effect of precursor solution concentration

Fe-doped Na_0.5Bi_0.5TiO₃ (NBTFe) thin films were prepared directly on indium tin oxide/glass substrates using a chemical solution deposition method combined with sequential layer annealing. The X-ray diffraction, scanning electron microscopy and insulating/ferroelectric/dielectric measurements were utilized to characterize the NBTFe thin films. All the NBTFe thin films prepared by four precursor solutions with various concentrations of 0.05, 0.10, 0.20 and 0.30 M exhibit polycrystalline perovskite structures with different relative intensities of (l00) peaks. A large remanent polarization (P_r) of 33.90 μC/cm² can be obtained in NBTFe film derived with 0.10 M spin-on solution due to its lower leakage current and larger grain size compared to those of other samples. Also, it shows a relatively symmetric coercive field and large dielectric tunability of 36.34%. Meanwhile, the NBTFe thin film with 0.20 M has a high energy-storage density of 30.15 J/cm³ and efficiency of 61.05%. These results indicate that the electrical performance can be controlled by optimizing the solution molarity.     

Effect of annealing temperature on ferroelectric electron emission of sol–gel PZT films

In this work, the influence of annealing temperature on the ferroelectric electron emission behaviors of 1.3-μm-thick sol–gel PbZr_0.52Ti_0.48O₃ (PZT) thin film emitters was investigated. The results revealed that the PZT films were crack-free in perovskite structure with columnar-like grains. Increasing annealing temperature led to the growth of the grains with improved ferroelectric and dielectric properties. The remnant polarization increased slightly from 35.3 to 39.6 μC/cm² and the coercive field decreased from the 56.4 to 54.6 kV/cm with increasing annealing temperature from 600 to 700 °C. The PZT film emitters exhibited remarkable ferroelectric electron emission behaviors at the threshold voltage above 95 V. The film annealed at 700 °C showed a relatively lower threshold voltage and higher emission current, which is related to the improved ferroelectric and dielectric properties at higher annealing temperature. The highest emission current achieved in this work was around 25 mA at the trigger voltage of 160 V.     

Structural and ferroelectric properties of chemical solution deposited (Nd,Cu) co-doped BiFeO3 thin film

Effects of (Nd, Cu) co-doping on the structural, electrical and ferroelectric properties of BiFeO₃ polycrystalline thin film have been studied. Pure and co-doped thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Significant improvements in the electrical and the ferroelectric properties were observed for the co-doped thin film. The remnant polarization (2P_r) and the coercive field (2E_c) of the co-doped thin film were 106 μC/cm² and 1032 kV/cm at an applied electric field of 1000 kV/cm, respectively. The improved properties of the co-doped thin film could be attributed to stabilized perovskite structures, reduced oxygen vacancies and modified microstructures.     

Structural and electrical properties of Na0.5Bi4.0RE0.5Ti4O15 (RE=Tm,Yb and Lu) thin films

In the current study, a series of lanthanide ions, Tm, Yb and Lu, were used for doping at the Bi-site of the Aurivillius phase Na_0.5Bi_4.5Ti₄O₁₅ (NaBTi) to investigate the structural, electrical and ferroelectric properties of the thin films. In this regard, Na_0.5Bi_4.5Ti₄O₁₅ and the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5i₄O₁₅ (RE=Tm, Yb and Lu, denoted by NaBTmTi, NaBYbTi, and NaBLuTi, respectively) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of the Aurivillius phase orthorhombic structures for all the thin films were confirmed by X-ray diffraction and Raman spectroscopic studies. Based on the experimental results, the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5Ti₄O₁₅ thin films exhibited a low leakage current and the improved ferroelectric properties. Among the thin films, the NaBLuTi thin film exhibited a low leakage current density of 6.96×10⁻⁷ A/cm² at an applied electric field of 100 kV/cm and a large remnant polarization (2P_r) of 26.7 μC/cm² at an applied electric field of 475 kV/cm.     

Enhanced multiferroic properties in Pr-doped BiFe0.97Mn0.03O3 films

Bi_1−xPr_xFe_0.97Mn_0.03O₃ (x=0.00, 0.05, 0.10, 0.15, 0.20) thin films were deposited on FTO/glass substrate using chemical solution deposition. The influences of Pr doping on the crystalline structure and multiferroic properties were investigated. In the X-ray diffraction and Raman spectra results, the crystal structures of Bi_1−xPr_xFe_0.97Mn_0.03O₃ films revealed a gradual transformation from the trigonal structure to the tetragonal structure. The leakage current densities of Bi_1−xPr_xFe_0.97Mn_0.03O₃ films are one order of magnitude lower than that of BiFeO₃. Compared with unsaturated polarization-electric field hysteresis loop of BiFeO₃ film, the Pr and Mn co-doped BFO films have significantly improved ferroelectric properties. The improved remnant polarization (Pr=91.3 µC/cm²) and the positive switching current (I=0.028 A) have been observed in Bi_0.85Pr_0.15Fe_0.97Mn_0.03O₃ film. The improved electrical properties are attributed to the structure transformation, increasing grain boundaries, low oxygen vacancies ratio and increasing Fe³⁺ concentration. In addition, the saturation magnetization of Bi_0.85Pr_0.15Fe_0.97Mn_0.03O₃ film is 1.81 emu/cm³, which is approximately three times higher than pure BiFeO₃ (M_s=0.67 emu/cm³).     

Electrical properties of chemical solution deposited (Bi0.9RE0.1)(Fe0.975Cu0.025)O3−δ (RE=Ho and Tb) thin films

Pure BiFeO₃ (BFO) and (Bi_0.9RE_0.1)(Fe_0.975Cu_0.025)O_3?δ (RE=Ho and Tb, denoted by BHFCu and BTFCu) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. The BHFCu and BTFCu thin films showed improved electrical and ferroelectric properties compared to pure BFO thin film. Among them, the BTFCu thin film exhibited large remnant polarization (2P_r), low coercive field (2E_c) and reduced leakage current density, which are 89.15 C/cm² and 345 kV/cm at 1000 kV/cm and 5.38×10^?5 A/cm² at 100 kV/cm, respectively.     

Pyroelectric,ferroelectric, piezoelectric and dielectric properties of Na0.5Bi0.5TiO3 ceramic prepared by sol-gel method

Sodium bismuth titanate (BNT) nanopowder of molar composition 50/50 (Na_0.5Bi_0.5TiO₃) was prepared by a sol-gel processing method. The structure and microstructure of the precursor gel as well as the ferroelectric, pyroelectric, dielectric and piezoelectric properties of the BNT were studied. BNT crystallized in the rhombohedra perovskites structure Na_0.5Bi_0.5TiO₃ was obtained from the precursor gel by heating at 700 °C for 2 h in air. The BNT ceramic at 1100 °C sintering temperature present high crystallinity, good dielectric properties at 1 kHz (ε′=885, tan δ=0.03, T_c=370 °C), piezoelectric properties (k₃₃=0.39, c₃₃=105 GPa, e₃₃=12.6 C/m², d₃₃=120 pC/N), high remnant polarization (P_r=47 μC/cm²) and pyroelectric coefficient ($p$=707 μC/m² K) and low coercive field (E_c=55 kV/cm). Hence, the BNT prepared by sol-gel method could be used for silicon based memory device application where a low synthesis temperature is a key requirement.     

Biocompatible Aurivillius-like layered ferroelectric BaIn2Ta2O9

A biocompatible Aurivillius-like layered ferroelectric that was designed by first-principles analysis and its thin film fabricated using radio frequency magnetron sputtering has been utilized for sensors of biomedical microelectromechanical systems. Aurivillius ferroelectrics have superior characteristics such as ferroelectric anisotropies and high Curie temperatures, and are widely used for sensors and memories. However, they contain the bio-toxic element, bismuth. In this study, we designed and fabricated a new biocompatible Aurivillius-like ferroelectric. SrBi₂Ta₂O₉ was subjected to first-principles calculation for validation. Lattice parameters of SrBi₂Ta₂O₉ in each phase and the spontaneous polarization value were in good agreement with the experimental reports. Subsequently, the prediction of Aurivillius-like materials and generation of its thin films were performed. During the design of the new molecule, 37 candidates were obtained by including constraint conditions such as the tolerance factor. We carried out the first-principles calculations for the structure optimization, determination of the band gap (for insulation), the soft mode (for ferroelectric phase transition), and the ferroelectric properties. The spontaneous polarization of BaIn₂Ta₂O₉ was calculated as 7.95 nC/cm². Next, a BaIn₂Ta₂O₉ thin film was generated. Through the experimental design procedure using an L₂₇ orthogonal array, we determined the sputtering conditions. Introducing the post-annealing process, the polarization-electric field hysteresis loop was obtained and its remnant polarization was calculated to be 15 nC/cm². The x-ray diffraction pattern predicted the crystal structure of SrBi₂Ta₂O₉-type materials. These results show the possible formation of the biocompatible Aurivillius-like ferroelectric material, BaIn₂Ta₂O₉.     

Influence of seed layer on crystal orientation and electrical properties of (Na0.85K0.15)0.5Bi0.5TiO3 thin films prepared by a sol–gel process

Sol–gel derived lead-free (Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (NKBT) thin films, with and without a Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ (PLCT) seed layer, were fabricated on (111)Pt/Ti/SiO₂/Si substrates. The influences of the seed layer on crystal orientation and electrical properties were investigated in detail. XRD indicated that the NKBT thin films fabricated with a seed layer were fully crystallized into a single perovskite structure, while the films fabricated under the same conditions, but without a seed layer, possessed a certain amount of pyrochlore phase. The NKBT film with a 14 nm-thick seed layer showed high (100) orientation, and exhibited enhanced electrical properties, such as a higher remanent polarization (Pr～18 µC/cm²), a lower dielectric loss tangent (tan δ ～0.023) and smaller transient current density (J<10^?5 A/cm²).     

Effects of annealing temperature on the microstructure,ferroelectric and dielectric properties of W-doped Na0.5Bi0.5TiO3 thin films

The effects of annealing temperature on the structure, morphology, ferroelectric and dielectric properties of Na_0.5Bi_0.5Ti_0.99W_0.01O_3+δ (NBTW) thin films are reported in detail. The films are deposited on indium tin oxide/glass substrates by a sol-gel method and the annealing temperature adopted is in the range of 560–620 °C. All the films can be well crystallized into phase-pure perovskite structures and show smooth surfaces without any cracks. Particularly, the NBTW thin film annealed at 600 °C exhibits a relatively large remanent polarization (P_r) of 20 μC/cm² measured at 750 kV/cm. Additionally, it shows a high dielectric constant of 608 and a low dielectric loss of 0.094 as well as a large dielectric tunability of 62%, making NBTW thin film ideal in the room-temperature tunable device applications.     

Tunable multiferroic properties of Mn substituted BiFeO3 thin films

The current study explored the influence of Mn substitution on the electrical and magnetic properties of BiFeO₃ (BFO) thin films synthesized using low cost chemical solution deposition technique. X-ray diffraction analysis revealed that pure rhombohedral phase of BiFeO₃ was transformed to the tetragonal structure with P4mm symmetry on Mn substitution. A leakage current density of 5.7×10⁻⁴ A/cm² which is about two orders of magnitude lower than pure BFO was observed in 3% Mn doped BFO thin film at an external electric field >400 kV/cm. A well saturated (p-E) loops with saturation polarization (P_sat) and remanent polarization (2P_r) as high as 60.34 µC/cm² and 25.06 µC/cm² were observed in 10% Mn substituted BFO thin films. An escalation in dielectric tunability (n_r), figure of merit (K) and quality factor (Q) were observed in suitable Mn doped BFO thin films. The magnetic measurement revealed that Mn substituted BFO thin films showed a large saturation magnetization compared to pure BFO thin film. The highest saturation ~31 emu/cc was observed for 3% Mn substituted BFO thin films.     

Effects of Tb doping on structural and electrical properties of 47(Ba0.7Ca0.3)TiO3–0.53Ba(Zr0.2Ti0.8)O3 thin films at various annealing temperature by pulsed laser deposition

The ceramic thin films of 47(Ba_0.7Ca_0.3)TiO₃–0.53Ba(Zr_0.2Ti_0.8)O₃ (BCZT) + x (x = 0.2, 0.3, 0.4 and 0.5) mol% Tb were grown on Pt(111)/Si substrates with various annealing temperature by pulsed laser deposition. The XRD spectra confirm that Tb element can enhance the (l10) and (111) orientations in ceramic films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that Tb-doping can increase particle size effectively. The surface of Tb-doped film annealed at 800 ℃ is uniform and crack-free, and the average particle size and mean square roughness (RMS) are about 280 nm and 4.4 nm, respectively. Comparing with pure BCZT, the residual polarization (P_r) of 0.4 mol% Tb-doped film annealed at 800 ℃ increase from 3.6 to 9.8 μC/cm². Moreover, the leakage current density value of Tb doped films are one order of magnitude (5.33 × 10^?9?1.97 × 10^?8 A/cm² under 100 kV/cm) smaller than those of pure BCZT films (1.02 × 10^?7 A/cm²).     

Structural and electrical properties of Pb(Zr0.53Ti0.47)O3 films prepared on La0.5Sr0.5CoO3 coated Si substrates

PbZr_0.53Ti_0.47O₃ (PZT) thin films with thickness of 0.9 μm were prepared on La_0.5Sr_0.5CoO₃ (LSCO) coated Si substrates. Both PZT and LSCO were prepared by the sol–gel method. The concentration of LSCO sol was varied from 0.3 to 0.1 mol/L, which could modify the preferential orientation of PZT thin films and consequently affect the dielectric and ferroelectric properties. The LSCO electrode layers derived from lower sol concentration of 0.1 mol/L have much more densified structure, which facilitates the formation of (1 0 0) textured PZT films with smooth and compact columnar grains. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm², respectively.     

Synthesis and characterizations of BNT–BT and BNT–BT–KNN ceramics for actuator and energy storage applications

Dielectric and ferroelectric properties of 0.93Bi_0.5Na_0.5TiO₃–0.07BaTiO₃ (BNT–BT) and 0.93Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–0.01K_0.5Na_0.5NbO₃ (BNT–BT–KNN) ceramics were studied in detail. An XRD analysis confirmed the single perovskite phase formation in both the samples. Room temperature (RT) dielectric constant (ε_r) ~1020 and 1370, respectively at 1 kHz frequency were obtained in the BNT–BT and BNT–BT–KNN ceramics. Temperature dependent dielectric and the polarization vs. electric field (P–E) studies confirmed the coexistence of ferroelectric (FE) and anti-ferroelectric (AFE) phases in the BNT–BT and BNT–BT–KNN ceramics. Substitution of KNN into the BNT–BT system decreased the remnant polarization, coercive field and the maximum strain percentage. The energy storage density values ~0.485 J/cm³ and 0.598 J/cm³ were obtained in the BNT–BT and BNT–BT–KNN ceramics, respectively. High induced strain% in the BNT–BT ceramics and the high energy storage density in the BNT–BT–KNN ceramics suggested about the usefulness of these systems for the actuator and the energy storage applications, respectively.     

Dielectric and optical properties of electroceramic PBZNZT thin films prepared by pulsed laser deposition process

The 0.6[0.94Pb(Zn_1/3Nb_2/3)O₃ + 0.06BaTiO₃] + 0.4[0.48(PbZrO₃) + 0.52(PbTiO₃)], PBZNZT, thin films were synthesized by pulsed laser deposition (PLD) process. The PBZNZT films possess higher insulating characteristics than the PZT (or PLZT) series materials due to the suppressed formation of defects, therefore, thin-film forms of these materials are expected to exhibit superior ferroelectric properties as compared with the PZT (or PLZT)-series thin films. Moreover, the Ba(Mg_1/3Ta_2/3)O₃ thin film of perovskite structure was used as buffer layer to reduce the substrate temperature necessary for growing the perovskite phase PBZNZT thin films. The PBZNZT thin films of good ferroelectric and dielectric properties (remanent polarization P_r = 26.0 μC/cm², coercive field E_c = 399 kV/cm, dielectric constant K = 737) were achieved by PLD at 400 °C. Such a low substrate temperature technique makes this process compatible with silicon device process. Moreover, thus obtained PBZNZT thin films also possess good optical properties (about 75% transmittance at 800 nm). These results imply that PBZNZT thin films have potential in photonic device applications.