Preparation and ferroelectric properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 thin films deposited on Pt electrodes using LaNiO3 as buffer layer

(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ thin films were deposited on Pt/Ti/SiO₂/Si (1 1 1) and LaNiO₃/Pt/Ti/SiO₂/Si (1 1 1) substrates by a sol–gel process. The phase structure and ferroelectric properties were investigated. The X-ray diffraction pattern indicated that the (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ thin film deposited on Pt/Ti/SiO₂/Si (1 1 1) substrates is polycrystalline structure without any preferred orientation. But the thin film deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates shows highly (1 0 0) orientation (f ≥ 81%). The leakage current density for the two thin films is about 6 × 10^?3 A/cm² at 250 kV/cm, and thin film deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates possessed a much lower leakage current under high electric field. The hysteresis loops at an applied electric field of 300 kV/cm and 10 kHz were acquired for the thin films. The thin films deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates showed improved ferroelectricity.     

Enhanced ferroelectric properties of Ce-substituted BiFeO3 thin films on LaNiO3/Si substrates prepared by sol–gel process

The effects of Ce substitution on the structural and electrical properties of multiferroic BiFeO₃ thin films grown on LaNiO₃/Si(1 0 0) substrates by a sol–gel process have been reported. X-ray diffraction data confirmed the substitutions of Ce into the Bi site with the elimination of all secondary phases under a substitution ratio x = 15%. The dielectric constants of the films increased from 90 to ～260 below 100 kHz with 5% molar Ce substitution and the films showed enhanced dielectric behavior. We observed a substantial increase in the remnant polarization (P_r) with Ce substitution and obtained a maximum value of ～71 μC/cm² by 5% molar Ce incorporation. The leakage current behavior at room temperature of the films was studied and it was found that the leakage current density decreased from 10^?6 to 10^?8 A/cm² for 5% molar Ce-substituted films under a field 150 kV/cm. The reduction of dc leakage current of Ce-substituted films is explained on the basis of relative phase stability and improved microstructure of the material.     

Composition dependent structure,dielectric and energy storage properties of Pb(Tm1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3 antiferroelectric ceramics

In order to stabilize the perovskite structure and improve the storage energy density (U) of Pb(Tm_1/2Nb_1/2)O₃ (PTmN) based materials, Pb(Mg_1/3Nb_2/3)O₃ (PMN) was introduced into PTmN to form binary (1-x)PTmN-xPMN solid solution ceramics. The XRD patterns show that all the compositions belong to orthorhombic phase with space group Pbnm. The Curie temperature (T_C) gradually decreases while the dielectric constant (ε') increases for (1-x)PTmN-xPMN with increasing PMN content. The ε' of each composition above T_C obeys the Curie-Weiss law. The appearance double hysteresis loop confirms the antiferroelectric nature of (1-x)PTmN-xPMN (x = 0.02–0.18) ceramics. With the increase of PMN concentration, the maximum polarization slowly increases from 8.58 μC/cm² to 29.5 μC/cm² while the threshold electric field (E_A-F) gradually declines from 290 kV/cm to 120 kV/cm. The maximum of U (3.12 J/cm³) is obtained in 0.92PTmN-0.08PMN ceramic with moderate E_A-F = 220 kV/cm, which makes (1-x)PTmN-xPMN ceramics safe in practical application.     

Enhancement of electrical properties of (Gd,V) co-doped BiFeO3 thin films prepared by chemical solution deposition

Pure BiFeO₃ (BFO) and (Bi_0.9Gd_0.1)(Fe_0.975V_0.025)O_3+δ(BGFVO) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. The improved electrical properties were observed in the BGFVO thin film. The leakage current density of the co-doped BGFVO thin film showed two orders lower than that of the pure BFO, 8.1×10^?5 A/cm² at 100 kV/cm. The remnant polarization (2P_r) and the coercive electric field (2E_c) of the BGFVO thin film were 54 μC/cm² and 1148 kV/cm with applied electric field of 1100 kV/cm at a frequency of 1 kHz, respectively. The 2P_r values of the BGFVO thin film show the dependence of measurement frequency, and it has been fairly saturated at about 30 kHz.     

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.     

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.     

Dielectric and piezoelectric properties of lead-free (K0.44Na0.46)NbO3-0.5%MnO2 single crystals grown by the TSSG method

Lead-free (K_0.44Na_0.46)NbO₃-0.5%MnO₂ (KNN-0.5%MnO₂) single crystals with dimensions of Ф30×10 mm were successfully grown by a top seeded solution growth technique (TSSG). The X-ray diffraction pattern has shown that the as-grown crystals have an orthorhombic perovskite structure. The orthorhombic-tetragonal (T_O-T) and tetragonal-cubic phase transition temperature (the Curie temperature T_C) of the single crystal were found at 184 °C and 412 °C, respectively. The KNN-0.5%MnO₂ single crystals exhibited high piezoelectric constants d₃₃ and dielectric permittivity ε_r, being 261 pC/N and 275. Well saturated P-E hysteresis loop with remnant polarization P_r=22.06 µC/cm² and coercive field E_c=17.93 kV/cm was obtained at a maximum electric field of 3 kV/mm. A high strain (0.24%) and electromechanical coupling coefficient K_t (65.9%) were obtained along the (001) orientation. These excellent results indicated that the KNN-0.5%MnO₂ single crystals could be used as high quality lead-free material.     

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.     

Lead-free BaTiO3-Bi0.5Na0.5TiO3-Na0.73Bi0.09NbO3 relaxor ferroelectric ceramics for high energy storage

A series of (1-x)(0.65BaTiO₃-0.35Bi_0.5Na_0.5TiO₃)-xNa_0.73Bi_0.09NbO₃ ((1-x)BBNT-xNBN) (x = 0–0.14) ceramics were designed and fabricated using the conventional solid-state sintering method. The microstructure, dielectric property, relaxor behavior and energy storage property were systematically investigated. X-ray diffraction results reveal a pure perovskite structure and dielectric measurements exhibit a relaxor behavior for the (1-x)BBNT-xNBN ceramics. The slim polarization electric field (P-E) loops were observed in the samples with x ≥ 0.02 and the addition of Na_0.73Bi_0.09NbO₃ (NBN) could decrease the remnant polarization (P_r) of the (1-x)BBNT-xNBN ceramics obviously. The sample with x = 0.08 exhibits the highest energy storage density of 1.70 J/cm³ and the energy storage efficiency of 82% at 172 kV/cm owing to its submicron grain size and high relative density. These results show that the (1-x)BBNT-xNBN ceramics may be promising lead-free materials for high energy storage density capacitors.     

Energy storage and release properties of Sr-doped (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics

Pb_0.94−xLa_0.04Sr_x[(Zr_0.6Sn_0.4)_0.84Ti_0.16]O₃ (x=0,0.02,0.04,0.06) antiferroelectric ceramics were fabricated via conventional solid-state reaction. The increase of Sr content enhanced the stability of antiferroelectric phase, which resulted in the rise of phase transition fields and energy density. When x=0.06, the releasable energy density was 1.52 J/cm³ and the efficiency was 93.3% under 129 kV/cm. The pulsed discharge current was also measured to evaluate the energy release properties. Under 129 kV/cm, the obtained current density could be as high as 165.5 A/cm². The pulsed discharge energy density was 1.21 J/cm³ and 90% of that could be released in less than 200 ns. The high energy density, high efficiency and fast energy release time indicate that the obtained AFE ceramics are very promising for pulsed power capacitors.     

Enhanced electrocaloric effect and energy-storage performance in PBLZT films with various Ba2+ content

(100)-oriented Pb_(0.90−x)Ba_xLa_0.10Zr_0.90Ti_0.10O₃ (x=0, 0.02, 0.05 and 0.11) antiferroelectric thick films were deposited on LaNiO₃/Si (100) substrates by the sol-gel process. The influences of Ba²⁺ content on the dielectric properties, electrocaloric effect (ECE), energy-storage performance and leakage current were systematically investigated. With Ba²⁺ content increasing, the temperature (T_m) corresponding to the maximum dielectric constant of the thick films was decreased, while their diffuseness was increased. The maximum ECE ∆T=18.1 °C was obtained in the thick film with x=0.05 at room temperature under ∆E=700 kV/cm. The maximum energy storage density of 42.3 J/cm³ and the corresponding efficiency of 68% was achieved in the film with x=0.11, companied by a power density of 0.53 MW/cm³, due to its high breakdown strength. In addition, a small leakage current density (<10⁻⁵ A/cm²) were attained in these films at room temperature. In conclusion, we believe that this kind of antiferroelctric thick film is a potential candidate for applications in solid cooling devices and the energy-storage systems.     

Synthesis and characterizations of KNN ferroelectric ceramics near 50/50 MPB

Lead free ferroelectric ceramics near the morphotropic phase boundary (MPB) of K_xNa_1?x(NbO₃)/KNN system (where x=0.48, 0.50, 0.52) were synthesized in the single perovskite phase by the partial co-precipitation synthesis route. The compositional dependences of phase, structure and electrical properties were studied in detail. X-ray diffraction (XRD) study revealed the coexistence of orthorhombic and monoclinic structures in K_0.50N_0.50NbO₃. SEM characterization of the sintered KNN ceramics revealed dense and homogeneous packing of grains. Room temperature (RT) dielectric constant (ε_r) ～648, dielectric loss (tan δ) ～0.05 at 100 kHz, a relatively high density (ρ) ～4.49 g/cm³, remnant polarization (P_r) ～11.76 μC/cm², coercive field (E_c) ～9.81 kV/cm, Curie temperature (T_c) ～372 °C and piezoelectric coefficient (d₃₃) ～71 pC/N observed in K_0.50N_0.50NbO₃ suggested that it can be an important lead free ferroelectric material.     

Effects of Mn doping on dielectric properties and energy-storage performance of Na0.5Bi0.5TiO3 thick films

Lead-free Na_0.5Bi_0.5Ti_1−xMn_xO₃ (NBTMn_x, x=0, 0.01, 0.03 and 0.05) ferroelectric thick films have been fabricated on LaNiO₃/Si(100) substrate by using a polyvinylpyrrolidone-modified sol-gel method and the effects of Mn content on their microstructure, dielectric properties and energy-storage performance were investigated. Compared with the pure Na_0.5Bi_0.5TiO₃ (NBT) thick films, NBTMn_x thick films exhibited a large enhancement in dielectric properties and energy-storage performance. Particularly, a giant recoverable energy-storage density (W) of 30.2 J/cm³ and the corresponding efficiency (η) of 47.7% were obtained in NBTMn_0.01 thick film at 2310 kV/cm. Moreover, the NBTMn_0.01 thick film displayed good energy-storage stability over a large temperature range at different frequency.     

Impact of Sr-doping on structural and electrical properties of Pb(Zr0.52Ti0.48)O3 thin films on RuO2 electrodes

In this paper, we investigated the impact of Sr-doping on the structural properties and electrical characteristics of lead zirconate titanate [Pb(Zr_0.52Ti_0.48)O₃, PZT] thin films deposited on RuO₂ electrodes by a sol-gel process and spin-coating technique. We used X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and field-emission transmission electron microscopy to explore the structural, morphological, chemical, and microstructural features, respectively, of these films as a function of the growth condition (strontium doping concentrations varied from 1, 3, and 5 mol%). The PZT thin film processed at the 3 mol% Sr exhibited the best electrical characteristics, including a low leakage current of 2.27×10⁻⁷ A/cm² at an electric field of 50 kV/cm, a large capacitance value of 2.74 μF/cm² at a frequency of 10 kHz, and a high remanent polarization of 37.95 μC/cm² at a frequency of 5 kHz. We attribute this behavior to the optimal amount of strontium in the PZT film forming a perovskite structure and a thicker interfacial layer at the PSZT film-RuO₂ electrode interface.     

Synthesis of (K,Na) (Nb,Ta)O3 lead-free piezoelectric ceramic powders by high temperature mixing method under hydrothermal conditions

A facile hydrothermal route via high temperature mixing method was used to synthesize (K, Na) (Nb, Ta)O₃ lead-free piezoelectric ceramic powders. The influence of Ta doping and K⁺/(K⁺ + Na⁺) molar ratios in the starting solution on the resultant powders were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The Ta element was successfully doped into the alkaline niobate structure to form crystalline (K, Na) (Nb, Ta)O₃ lead-free piezoelectric ceramics powder. The microstructure, piezoelectric, ferroelectric, and dielectric properties of the sintered (K, Na) (Nb, Ta)O₃ ceramics from the obtained powders were investigated. The piezoelectric coefficient (d₃₃), electromechanical coupling coefficient (k_p), dielectric constant (?_r), and remnant polarization (P_r) of the sample sintered at 1180 °C show optimal values of 210 pC/N, 34.0%, 2302, and 19.01 μC/cm², respectively.     

Preparation and electrical properties of Bi2Zn2/3Nb4/3O7 thin films deposited at room temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited at room temperature on Pt/Ti/SiO₂/Si(1 0 0) and polymer-based copper clad laminate (CCL) substrates by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited in situ with no intentional heating under an oxygen pressure of 4 Pa and then post-annealed at 150 °C for 20 min. It was found that the films are still amorphous in nature, which was confirmed by the XRD analysis. It has been shown that the surface roughness of the substrates has a significant influence on the electrical properties of the dielectric films, especially on the leakage current. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates exhibit superior dielectric characteristics. The dielectric constant and loss tangent are 59.8 and 0.008 at 10 kHz, respectively. Leakage current density is 2.5 × 10^?7 A/cm² at an applied electric field of 400 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on CCL substrates exhibit the dielectric constant of 60 and loss tangent of 0.018, respectively. Leakage current density is less than 1 × 10^?6 A/cm² at 200 kV/cm.     

Structural and electrical properties of sol–gel-derived Al-doped bismuth ferrite thin films

Al-doped BiFeO₃ (BiFe_(1?x)Al_xO₃) thin films with small doping content (x=0, 0.05, and 0.1) were grown on Pt(111)/TiO₂/SiO₂/Si substrates at the annealing temperature of 550 °C for 5 min in air by the sol–gel method. The crystalline structure, as well as surface and cross section morphology were studied by X-ray diffraction and scanning electron microscope, respectively. The dielectric constant of BiFeO₃ film was approximately 71 at 100 kHz, and it increased to 91 and 96 in the 5% and 10% Al-doped BiFeO₃ films, respectively. The substitution of Al atoms in BiFeO₃ thin films reduced the leakage current obviously. At an applied electric field of 260 kV/cm, the leakage current density of the undoped BiFeO₃ films was 3.97×10^?4 A/cm², while in the 10% Al-substitution BiFeO₃ thin films it was reduced to 8.4×10^?7 A/cm². The obtained values of 2P_r were 63 μC/cm² and 54 μC/cm² in the 5% and 10% Al-doped BiFeO₃ films at 2 kHz, respectively.     

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.     

Optical and electrical properties of pressureless sintered transparent (K0.37Na0.63)NbO3-based ceramics

Lead-free (1−x)(K_0.37Na_0.63)NbO₃-xCa(Sc_0.5Nb_0.5)O₃ (x=0.050, 0.070, 0.090, 0.095 and 0.100) transparent ferroelectric ceramics have been fabricated by pressureless sintering procedure. Transmittance of 0.91(K_0.37Na_0.63)NbO₃-0.09Ca(Sc_0.5Nb_0.5)O₃ ceramics sintered in sealed alumina crucible was 15% higher than those sintered unsealed in air. By increasing the content of Ca(Sc_0.5Nb_0.5)O₃, the phase structure of (K_0.37Na_0.63)NbO₃ ceramics transformed from orthorhombic to tetragonal symmetry first and then to pseudo cubic symmetry. The 0.91(K_0.37Na_0.63)NbO₃-0.09Ca(Sc_0.5Nb_0.5)O₃ ceramics exhibited high density (98%), high transmittance (60%) in the near-IR region and relatively good electrical properties (ε_r=1914, tanδ=0.037, T_c=147 °C, P_r=6.88 μC/cm², E_c=8.49 kV/cm). Meanwhile, the introduction of Ca(Sc_0.5Nb_0.5)O₃ induced a composition fluctuation in the (K_0.37Na_0.63)NbO₃ lattice and made the ceramics more relaxor-like, which would lead to a further reduction of light scattering. These results demonstrated that 0.91(K_0.37Na_0.63)NbO₃-0.09Ca(Sc_0.5Nb_0.5)O₃ could be promising lead-free transparent ferroelectric ceramics.     

Effect of repeated composite sol infiltrations on the dielectric and piezoelectric properties of a Bi0.5(Na0.82K0.18)0.5TiO3 lead free thick film

Bi_0.5(Na_0.82K_0.18)_0.5TiO₃ lead free thick films have been produced using a combination of screen printing and subsequent infiltration of corresponding composite sol. Their structure, dielectric, ferroelectric and piezoelectric properties were investigated with variation in the number of composite sol infiltrations and the nanopowder loading in composite sol. Dielectric constant, remanent polarization, and piezoelectric coefficient have been shown to increase with increasing numbers of composite sol infiltration. Dielectric and ferroelectric properties of the thick films are found to be strongly dependent on the powder concentration of composite sols. The resulting 40 μm thick films infiltrated with 1.5 g/ml composite sols have maximum relative permittivity of 569 (at 10 kHz), remanent polarization of 21.3 μC/cm², coercive field of 80 kV/cm, and longitudinal effective piezoelectric coefficient d_33eff of 109 pm/V. The performance of these lead free piezoelectric thick films is comparable to the corresponding bulk ceramics.