Lead-free Ferroelectric Bi0 Research Articles

Magnetic and optical properties of new (1 − x)Bi0.5Na0.5TiO3 + x CaMnO3−δ solid solution materials

CaMnO3-δ-modified Bi0.5Na0.5TiO3 was fabricated by using a sol–gel method. In the modified Bi0.5Na0.5TiO3, a single perovskite with distorted structure was obtained due to the random distribution of Ca and Mn cations in the host lattice. The co-modification in A- and B-sites of Bi0.5Na0.5TiO3 via Ca and Mn resulted in the reduction of optical band gap and induction of room-temperature ferromagnetism. Co-modification of A- and B-sites in lead-free ferroelectric Bi0.5Na0.5TiO3 is suitable for fabricating smart materials in electronic devices.

Spectroscopic study of phase transitions in ferroelectric Bi0.5Na0.5Ti1−xMnxO3−δ films with enhanced ferroelectricity and energy storage ability

Lead-free ferroelectric Bi0.5Na0.5TiO3 (BNT) has attracted considerable attention taking into account environment issues and applications in micro electro mechanical systems. The effects of manganese (Mn) substitution on microstructure, lattice dynamics, and optical properties of BNT films have been investigated by X-ray diffraction, Raman scattering and ellipsometric spectra. The phase transitions as a function of temperature have been systemically explored by temperature-dependent Raman and ellipsometric spectra. The anomalous temperature-dependent behavior of Raman-active modes suggests that there is an intermediate phase between ferroelectric rhombohedral and paraelectric tetragonal phase, which is confirmed by the temperature-dependent optical band gap (Eg) and extinction coefficient (κ) extracted from ellipsometric spectra analysis. And then, a phase diagram as a function of Mn composition has been proposed. Finally, we demonstrate that Mn-dopant is an effective approach to enhance ferroelectric properties, improve energy storage ability, and increase permittivity as well as suppress leakage current. Electrical dielectric responses indicate that there is a critical frequency and polarization relaxation behavior in the films. The present results will be helpful for the application of BNT-based lead-free multifunctional devices.

Room-temperature ferromagnetism in Fe-based perovskite solid solution in lead-free ferroelectric Bi0.5Na0.5TiO3 materials

The integration of ferromagnetism in lead-free ferroelectric materials is important to fabricate smart materials for electronic devices. In this work, (1 − x)Bi0.5Na0.5TiO3 + xMgFeO3-δ materials (x = 0–9 mol%) were prepared through sol–gel method. X-ray diffraction characterization indicated that MgFeO3-δ materials existed as a well solid solution in lead-free ferroelectric Bi0.5Na0.5TiO3 materials. The rhombohedral structure of Bi0.5Na0.5TiO3 materials was distorted due to the random distribution of Mg and Fe cations into the host lattice. The reduced optical band gap and the induced room-temperature ferromagnetism were due to the spin splitting of transition metal substitution at the B-site of perovskite Bi0.5Na0.5TiO3 and the modification by A-site co-substitution. This work elucidates the role of secondary phase as solid solution in Bi0.5Na0.5TiO3 material for development of lead-free multiferroelectric materials.

Defect induced room temperature ferromagnetism in lead-free ferroelectric Bi0.5K0.5TiO3 materials

Development the multiferroic materials based on the lead-free ferroelectric materials is the new possible channel to create the next generation devices. The pure Bi0.5K0.5TiO3 and Mn-doped Bi0.5K0.5TiO3 materials were synthesized using sol-gel method. While the substitution of Mn for Ti site reduces the optical band gap in Bi0.5K0.5TiO3, the room temperature ferromagnetism is obtained in both un-doped and Mn-doped Bi0.5K0.5TiO3 materials. By means of the first-principles calculations, the ferromagnetism in Mn-doped Bi0.5K0.5TiO3 materials can be explained by the mixed valence states of Mn ions through the crystal field mechanism and that in un-doped Bi0.5K0.5TiO3 materials is ascribed to the formation of O or Ti vacancies during the sample growth.

Structural, Optical, and Magnetic Properties of Lead-Free Ferroelectric Bi0.5K0.5TiO3 Solid Solution with BiFeO3 Materials

A solid solution of Bi0.5K0.5TiO3-BiFeO3 was fabricated by a sol–gel technique. The pure Bi0.5K0.5TO3 samples exhibited weak room-temperature ferromagnetism. The room-temperature ferromagnetism was observed in BiFeO3 solid solution in Bi0.5K0.5TiO3. The optical band gap of Bi0.5K0.5TiO3 was reduced from 3.22 eV to 1.39 eV with the increase in the amount of BiFeO3 solid solution. The room-temperature ferromagnetism and band gap reduction were attributed to the diffusion of BiFeO3 into Bi0.5K0.5TiO3 to form a solid solution. Our work provided a simple method of realizing room-temperature ferromagnetism in lead-free ferroelectric materials.

Origin of Room Temperature Ferromagnetism in Cr-Doped Lead-Free Ferroelectric Bi0.5Na0.5TiO3 Materials

The development of multiferroic materials based on lead-free ferroelectric material provides an opportunity to fabricate next-generation electronic devices. In this work, Cr-doped lead-free ferroelectric Bi0.5Na0.5TiO3 materials were synthesized by using the sol–gel method. The optical band gap was reduced from 3.12 eV to 2.12 eV for undoped and 9 mol.% Cr-doped Bi0.5Na0.5TiO3 with the substitution of Cr at the Ti-site. Cr-doped Bi0.5Na0.5TiO3 materials exhibited weak ferromagnetism at room temperature. Saturation magnetization was approximately 0.08 μ B/Cr at 5 K. Our work will facilitate the further understanding of the role of transition metal ferromagnetism in lead-free ferroelectric materials at room temperature.

Making room-temperature ferromagnetism in lead-free ferroelectric Bi0.5Na0.5TiO3 material

We have successfully fabricated Mn-doped wide band gap lead-free ferroelectric Bi0.5Na0.5TiO3 by sol-gel technique. The band gap reduced from 3.12 to 1.71eV as increasing doping Mn concentration level up to 9mol%. The room temperature ferromagnetism in Mn-doped Bi0.5Na0.5TiO3 samples was observed. The magnetic moment was around 2.69μB/Mn at 5K. We expected that this work will open the new direction for advance function of lead-free ferroelectric materials.

Processing and properties of ferroelectric Bi0.5(Na0.65K0.35)0.5TiO3 ceramics under the effect of different sintering temperature

Lead-free ferroelectric Bi0.5(Na0.65K0.35)0.5TiO3 ceramic was synthesized after optimizing the sintering temperature in the range 1070–1110 °C. The best dielectric, ferroelectric and piezoelectric values were obtained in the highly dense sample sintered at 1090 °C. A high dielectric constant (780 at 10 kHz at room temperature), high phase transition maxima (Tm = 330 °C) and conductivity mechanisms were reported. Good ferroelectric values in the P–E loop (Pr = 27.2 μC cm−2, Ec = 25 kV cm−1) with high piezoelectric coefficient (d33 = 132 pC N−1) and fatigue-free behavior were obtained.

Neutron total scattering studies on A-site disorder in lead-free ferroelectric Bi0.5(Na1–xKx)0.5TiO3

We performed neutron total scattering meas- urements on lead-free ferroelectric Bi0:5(Na1� xKx)0:5TiO3 (x ¼ 0:0, 0.25) and present local structures of A-site (Bi 3þ ,N a þ /K þ ) ions using reverse Monte Carlo modeling. The A-site incorporation of large K þ ions suppresses the tilting of oxygen octahedra and strongly influences the off-center displacement of A-site ions. As a result, we found that the Bi- -O bond length redistributes between x ¼ 0:0 and x ¼ 0:25. Compared to the Bi- -O bond, the distribution of Na/K- -O bond length was broader and smeared. Thus, the interplay between Bi 3þ and K þ ions plays a key role in ferroelectric response near morphotro- pic phase boundary. For the Ti- -O bond-length distribu- tion, we found little change between the two compositions despite the long-range symmetry difference. This result suggests that A-site and B-site off-center displacements are decoupled.