The relationship among dielectric anomaly, ferroelectric response, defects, and microstructures was established for (K0.48(1+x)Na0.52)0.95Li0.05Nb0.95Sb0.05O3 (x = 0.04, 0.00, −0.02, −0.04 and −0.08) ceramics. For x = −0.02 and −0.04, larger coercive fields and lower remnant polarizations were obtained; besides, an additional dielectric relaxation behavior was observed with the activation energy Ea being about 2.19 eV and 1.92 eV, respectively. Furthermore, the grain and grain boundary contributions to the capacitance were separated using impedance spectroscopy, which, combined with back-scattering characterization, firmly indicates the core–shell structure of K-deficient samples (x = −0.02 and −0.04). Unlike the cores, the shells possess a large amount of K+ vacancies (). This work paves a way for regulating the fine structure and more on the electrical properties of KNN-based materials.

The structural, magnetic and magnetoelectric properties were investigated for sol–gel prepared BaFe12O19 nanorods and plate-like nanoparticles. Based on comparative experiments with bulk ceramics, it is found that larger structural distortion is present in nanostructures, which could cause the enhancement of magnetocrystalline anisotropy and the off-center displacement of Fe3+ ions, and thus result in improved magnetic and magnetoelectric properties in BaFe12O19 plate-like nanoparticles. Meanwhile, the local (Fe2+–Fe3+) dipoles, which usually appear during a high temperature sintering process, can also contribute to the negative magnetoelectric effect of BaFe12O19 nanorods and a large room temperature magnetodielectric coefficient of about −13% is observed at 104 Hz and 9 kOe.

The effects of Fe ions incorporation into the Sr and Ti sites of SrTiO3 ceramics on the dielectric properties are studied in this work. It is found that the dielectric properties of the samples are sensitive to the components. Compared to SrTi0.9Fe0.1O3−δ with paraelectric property, Sr0.98Ti0.9Fe0.1O3−δ and Sr0.98Ti0.92Fe0.1O3−δ present dielectric relaxations at low temperature. After carefully analyzing the dielectric spectra by Arrhenius law and Power law, the dielectric relaxations are mainly attributed to the relaxation polarizations of defect dipoles formed by the off-center Fe ions at the Sr-sites and oxygen vacancies, and the dipole glass behavior are identified at low temperature.

Polycrystalline Bi3.25La0.75(Ti3−xFex/2Cox/2)O12 (0 ≤ x ≤ 0.5) ceramics are synthesized by the conventional solid state reaction method. Good ferroelectricity and weak ferromagnetism are obtained simultaneously at room temperature when x ≥ 0.2. The ceramics with x = 0.25 possess the best comprehensive properties, including high phase purity, large ferroelectric polarization, great dielectric constant, and also, larger remnant magnetization compared with other samples. Furthermore, significant dielectric anomalies appear near both the ferromagnetic Curie temperature and the spin glass freezing temperature. The possible magnetoelectric coupling mechanism is considered to be the associated binding effect of magnetic interaction on the migration of charged defects, especially oxygen vacancies.

We report the discovery of multiferroic behavior in double perovskite Y2NiMnO6. X-ray diffraction shows that the material has a centrosymmetric crystal structure of space group P21/n with Ni2+/Mn4+ ordering. This result is further confirmed by aberration-corrected scanning transmission electron microscopy combined with atomic resolution electron energy loss spectroscopy. The appearance of ferroelectric polarization coincides with the magnetic phase transition (∼67 K), which indicates that the ferroelectricity is driven by magnetism, and this is further confirmed by its strong magnetoelectric (ME) effect. We proposed the origin of the ferroelectricity is associated with the combination of Ni2+/Mn4+ charge ordering and the ↑↑↓↓ spin ordering. When compared with other known magnetic multiferroics, Y2NiMnO6 displays several attractive multiferroic properties, including high polarization (∼145 μC/m2), a high multiferroic transition temperature (∼67 K), and strong ME coupling (∼21%).Keywords: magnetoelectric effect; multiferroics; sol−gel; STEM; Y2NiMnO6;

We conducted a comparative study on structural, magnetic and electric properties of MnTiO3 ceramics sintered in air (MTO-A) and nitrogen (MTO-N) to explore the impact of oxygen vacancies (OVs) on them. The X-ray diffraction patterns show that MTO-N possesses a lattice contraction induced by OVs comparing with MTO-A. Distinct spin glass (SG) with Tsg (41 K) and magnetic exchange bias (EB) are only observed in the MTO-N sample. The results indicate that OVs may well lead to the enhanced magnetization, thereby generating SG behavior. Moreover, the dielectric characteristics of MTO-A and MTO-N are investigated additionally, two disparate relaxation mechanisms of Maxwell–Wagner relaxation and OVs migration are illuminated respectively, which further support the vital function of OVs.

KNb0.95Co0.05O3 (KN–Co) ceramic was prepared via a solid-state reaction method, and the effect of cobalt dopant on the structural, electric, and magnetic properties was studied. The KN–Co ceramic with polycrystalline perovskite structure exhibited ferromagnetic and ferroelectric properties simultaneously at room temperature, and the coupling of them was confirmed by a large magnetocapacitance effect (about 13%) near the Curie temperature. The possible causes for the magnetism and magnetoelectric properties are discussed.Highlights► We introduce a magnetic property to ferroelectric KNbO3 ceramic by Co doping. ► Room-temperature ferroelectric and ferromagnetic properties are obtained in KNb0.95Co0.05O3 ceramic. ► A magnetocapacitance effect of KNb0.95Co0.05O3 ceramic is observed.

Co and Nd co-substituted Bi5Ti3FeO15 thin films were prepared on Pt/Ti/SiO2/Si substrates via metal organic decomposition method. The structural and multiferroic properties of the films were investigated. It was found that Co ions enter into the lattice and occupy the Fe site. The Bi4.15Nd0.85Ti3Fe0.5Co0.5O15 films simultaneously exhibit ferroelectric and ferromagnetic properties at room temperature, and its 2Pr and 2Mr are 38 μC/cm2 and 3 kA/m, respectively. Moreover, substitutions create local ferromagnetic order and antiferromagnetic order depending on whether the local bonding is FeOCo or FeOFe/CoOCo, respectively. The competing interaction of the ferromagnetic and antiferromagnetic phases results in an interesting magnetic behavior of the films.Highlights► Co occupies the Fe site in Co-doped Bi4.15Nd0.85Ti3FeO15 (BNTF) film. ► Co doping enhances the ferromagnetism of BNTF due to local FeOCo interaction. ► 50% Co-doped BNTF film possesses room temperature ferroelectricity and ferromagnetism.

The magnetic and dielectric properties were investigated in the hexagonal YMnO3 ceramics synthesized by sol–gel method. An antiferromagnetic order about 70 K and a weak ferromagnetic order at 5 K have been detected in YMnO3 ceramics. In addition, we observed also the exchange-bias (EB) effect at low temperatures and it may originate from exchange coupling at the interface between ferromagnetic and antiferromagnetic orders for the co-existence of these two orders in some temperature region in hexagonal YMnO3. Furthermore, the dielectric measurements showed two thermally activated relaxation behaviors following the Arrhenius law in 290–430 K and above 500 K in YMnO3 ceramics and they can be explained as the dipolar effects associated with the charge carrier hopping between Mn2+ and Mn3+ and oxygen vacancy, respectively.HighlightsThe YMnO3 is a well-known multiferroic material, but many basic properties of this material are still not understood. In this manuscript, we report many magnetic and dielectric results including the antiferromagnetic and ferromagnetic orders that appeared at different temperatures; the EB effect and its origin. Also we have got the dielectric behaviors at different temperatures and have discussed the origin of the dielectric behaviors. All the results mentioned above are useful in the understanding of the multiferroic property of this well-known multiferroic material.

Sr1−xPrxTiO3 films were prepared by metal organic deposition method on (111) Pt/Ti/SiO2/Si substrates. Pr-doping greatly improves the dc leakage behavior of the films. The samples with x=0.075x=0.075 show excellent electric field frequency and temperature stability of dielectric properties, while the x=0.025x=0.025 samples indicate an obvious dielectric relaxation behavior and better polarization versus applied electric field (PP–EE) hysteresis loops. These peculiar electrical properties can be explained mainly by the Pr-doping-induced changes in the free charge carriers, the lattice distortion, the charge transfer process and polar nanoregions. In addition, the variable valence of Pr ions may also have significant impacts.

Strontium titanate films with high aa-axis orientation [a(100)=94.1%][a(100)=94.1%] and random orientation were deposited on (111) Pt/Ti/ SiO2/Si substrates by a concentration controlling of the precursor solution during the metal organic deposition process. Topography of samples was investigated by atomic force microscopy after annealing at 800 °C. X-ray diffraction found that the degree of aa-axis orientation increased with increasing annealing temperature. The leakage current and the dielectric property were strongly dependent on the film orientation, and the possible causes of orientation dependence were discussed.

The effects of external stress cooperated with temperature, measuring frequency and measuring electric field on the fatigue properties of Bi3.25La0.75Ti3O12 thin films are investigated. The fatigue properties can be improved by the external stress (both tensile and compressive). The larger the stress is, the more obvious the improvement is. Meanwhile, the stress-induced improvement is more distinct in the films annealed at a higher temperature. In addition, when measured at a higher frequency or at a larger electric field, the films show better fatigue properties, and the improvement caused by stress is more evident. The experimental results can be explained well by the mechanism in which the charged defects pin the domain walls during electric cycling.

Dense and flat SrZrO3 films in an orthorhombic (Pbnm) perovskite phase are fabricated on fused quartz substrates via the metal organic decomposition method. Optical measurements show that the average transmittance of the films is about 90% for light with a wavelength longer than 240 nm, and the absorption edge of the films shifts to longer wavelengths with an increase of annealing temperature and film thickness. Meanwhile, first-principles calculations are performed by using an accurate Vienna ab initio simulation package to explore the electronic band structure of orthorhombic SrZrO3. The observed shift of the absorption edge could be well explained by the size effect on the band structure.

Strontium titanate films with high a-axis orientation [a(100)=94.1%] and random orientation were deposited on (111) Pt/Ti/ SiO2/Si substrates by a concentration controlling of the precursor solution during the metal organic deposition process. Topography of samples was investigated by atomic force microscopy after annealing at 800 °C. X-ray diffraction found that the degree of a-axis orientation increased with increasing annealing temperature. The leakage current and the dielectric property were strongly dependent on the film orientation, and the possible causes of orientation dependence were discussed.

Sr1−xPrxTiO3 films were prepared by metal organic deposition method on (111) Pt/Ti/SiO2/Si substrates. Pr-doping greatly improves the dc leakage behavior of the films. The samples with x=0.075 show excellent electric field frequency and temperature stability of dielectric properties, while the x=0.025 samples indicate an obvious dielectric relaxation behavior and better polarization versus applied electric field (P–E) hysteresis loops. These peculiar electrical properties can be explained mainly by the Pr-doping-induced changes in the free charge carriers, the lattice distortion, the charge transfer process and polar nanoregions. In addition, the variable valence of Pr ions may also have significant impacts.

The effects of external stress cooperated with temperature, measuring frequency and measuring electric field on the fatigue properties of Bi3.25La0.75Ti3O12 thin films are investigated. The fatigue properties can be improved by the external stress (both tensile and compressive). The larger the stress is, the more obvious the improvement is. Meanwhile, the stress-induced improvement is more distinct in the films annealed at a higher temperature. In addition, when measured at a higher frequency or at a larger electric field, the films show better fatigue properties, and the improvement caused by stress is more evident. The experimental results can be explained well by the mechanism in which the charged defects pin the domain walls during electric cycling.

The relationship among dielectric anomaly, ferroelectric response, defects, and microstructures was established for (K0.48(1+x)Na0.52)0.95Li0.05Nb0.95Sb0.05O3 (x = 0.04, 0.00, −0.02, −0.04 and −0.08) ceramics. For x = −0.02 and −0.04, larger coercive fields and lower remnant polarizations were obtained; besides, an additional dielectric relaxation behavior was observed with the activation energy Ea being about 2.19 eV and 1.92 eV, respectively. Furthermore, the grain and grain boundary contributions to the capacitance were separated using impedance spectroscopy, which, combined with back-scattering characterization, firmly indicates the core–shell structure of K-deficient samples (x = −0.02 and −0.04). Unlike the cores, the shells possess a large amount of K+ vacancies (). This work paves a way for regulating the fine structure and more on the electrical properties of KNN-based materials.

Polycrystalline Bi3.25La0.75(Ti3−xFex/2Cox/2)O12 (0 ≤ x ≤ 0.5) ceramics are synthesized by the conventional solid state reaction method. Good ferroelectricity and weak ferromagnetism are obtained simultaneously at room temperature when x ≥ 0.2. The ceramics with x = 0.25 possess the best comprehensive properties, including high phase purity, large ferroelectric polarization, great dielectric constant, and also, larger remnant magnetization compared with other samples. Furthermore, significant dielectric anomalies appear near both the ferromagnetic Curie temperature and the spin glass freezing temperature. The possible magnetoelectric coupling mechanism is considered to be the associated binding effect of magnetic interaction on the migration of charged defects, especially oxygen vacancies.

The structural, magnetic and magnetoelectric properties were investigated for sol–gel prepared BaFe12O19 nanorods and plate-like nanoparticles. Based on comparative experiments with bulk ceramics, it is found that larger structural distortion is present in nanostructures, which could cause the enhancement of magnetocrystalline anisotropy and the off-center displacement of Fe3+ ions, and thus result in improved magnetic and magnetoelectric properties in BaFe12O19 plate-like nanoparticles. Meanwhile, the local (Fe2+–Fe3+) dipoles, which usually appear during a high temperature sintering process, can also contribute to the negative magnetoelectric effect of BaFe12O19 nanorods and a large room temperature magnetodielectric coefficient of about −13% is observed at 104 Hz and 9 kOe.