•Upconversion luminescence of In3+-doped Ba0.85Ca0.15TiO3:Er/Yb/In ceramics was firstly studied.•1.5% mol In3+ doping enhances the green emission intensity by 10 times.•In3+ doping is an effective way for enhancing upconversion luminescence.We synthesized In3+-doped Ba0.85Ca0.15TiO3:Er3+/Yb3+/xIn3+ lead-free ferroelectric ceramics that possess strong ferroelectricity and excellent upconversion luminescence under the excitation of 980 nm. With increasing x from 0, the green and red emission intensity increases and reaches the maximum at x=1.5% mol, then decreases slightly with further increase in x. For the x=1.5% sample the green emission intensity at 550 nm is ∼10 times larger than that of In3+ undoped samples. Such a large In3+ doping-induced enhancement of the luminescence is unprecedented for perovskite ferroelectrics. Based on the ultraviolet-visible-near infrared absorption spectra, the variation of the luminescence intensity with the In3+ content was discussed.

•0.6BiFeO3–0.4Bi0.5K0.5TiO3 shows a saturated polarization of 65.8 μC/cm2.•0.6BiFeO3–0.4Bi0.5K0.5TiO3 shows an enhanced d33 value due to its MPB.•(1−x)BiFeO3−xBi0.5K0.5TiO3(x = 0.3–1) shows a strong dielectric relaxor characteristic.The multiferroic (1−x)BiFeO3−xBi0.5K0.5TiO3 (BFO–xBKT) ceramic was prepared to investigate the dependence of its structural and electrical properties on BKT component. The ceramic processes a rhombohedral phase at 0 ≤ x ≤ 0.3 and a tetragonal phase at 0.5 ≤ x ≤ 1.0 while it owns the coexistence of these two phases at x∼0.4, according to the XRD patterns and the corresponding simulation with the Reitveld method. Specifically, BFO–0.4BKT shows a saturated polarization of 65.8 μC/cm2 and an enhanced piezoelectric d33 of 61 pC/N at room temperature which are much larger than those of other ceramics at x = 0–0.7. The dependence of dielectric constant on temperature suggests a strong relaxor characteristic and a high Curie temperature of ∼462 °C. Furthermore, the poled BFO–0.4BKT ceramic shows radial dielectric resonances at 20–300 °C due to the piezoelectric effect.

•La0.5Ba0.5MnO3 films were epitaxially grown on ternary ferroelectric single crystals.•Ferroelectric poling modifies the strain and physical properties of films.•Magnetic field enhances the strain effects of films.•Phase separation is crucial to understand the magnetic-field-tuned strain effect.We epitaxially grew La0.5Ba0.5MnO3 (LBMO) films on (001)- and (111)-oriented ferroelectric single-crystal substrates and reduced the in-plane tensile strain of LBMO films by poling the ferroelectric substrates along the 〈001〉〈001〉 or 〈111〉〈111〉 direction. Upon poling, a large decrease in the resistance and a considerable increase in the magnetization, Curie temperature, and magnetoresistance were observed for the LBMO film, which are driven by interface strain coupling. Such strain effects can be significantly enhanced by the application of a magnetic field. An overall analysis of the findings reveals that the mutual interaction between the strain and the magnetic field is mediated by the electronic phase separation which is sensitive to both strain and magnetic field. Our findings highlight that the electronic phase separation is crucial in understanding the electric-field-manipulated strain effects in manganite film/ferroelectric crystal heterostructures.

The multiferroic properties of BiFeO3-based ceramics were improved through optimizing their sintering method and doping with certain rare earth elements in pure BiFeO3. Some methods, especially liquid-phase sintering method has largely decreased the densities of oxygen vacancies and Fe2+ in BiFeO3-based ceramics, and thus their resistivity became high enough to measure the saturated polarization and the large piezoelectric d33 coefficient under the high electric field of >150 kV/cm. Besides, multiferroic properties were improved through the rare earth elements’ doping in pure BiFeO3. Magnetization commonly increases with the proportional increase of Nd, La, Sm and Dy contents up to ~30 %, while ferroelectric phase can transform to paraelectric phase at a certain proportion. An improved magnetoelectric coupling was often observed at ferroelectric phase with a relatively large proportion. Besides, an enhanced piezoelectric coefficient is expected in BiFeO3-based ceramics with morphotropic phase boundaries as they are already observed in thin epitaxial BiFeO3 films.

Both blue- and redshifts of resonant modes are observed in the rolled-up Y2O3/ZrO2 tubular microcavity during a conformal oxide coating process. Our investigation based on spectral analyses suggests that there are two competitive processes during coating: desorption of both chemically and physically absorbed water molecules and increase of the tube wall thickness. The redshift is due to the increase of the wall thickness and corresponding light confinement enhancement. On the other hand, desorption of water molecules by heating leads to a blueshift. The balance of these two factors produces the observed bi-directional shift of the modes while they both contribute to promoted quality factor after coating.

With a rhombohedra-like structure, the Bi0.875Sm0.125FeO3 ceramics show much-improved ferroelectric and piezoelectric properties: a saturated ferroelectric polarization of 40 μC/cm2 and a piezoelectric d33 of 45 pC/N at 20 °C. After the polarized sample was annealed at 600 °C, its d33 decreases to ∼20 pC/N. Besides, Bi0.875Sm0.125FeO3 shows dielectric or impedance resonances at 20–550 °C, suggesting that the ferroelectric component with high Curie temperature still partially remained at 550 °C. However, the impedance and the resistance decrease so fast with temperature increasing that both of them are below 1000 ohm above 420 °C. Even so, this piezoelectric resonance method can explore leaky ferroelectrics at high temperature.Highlights► Piezoelectric responses were observed at 20–550 °C in Bi0.875Sm0.125FeO3. ► Ferroelectric component partially remained at 700 °C. ► Both impedance and resistance were smaller than 1000 ohm above 420 °C.

Insulated Bi1 − xDyxFeO3 (x = 0–0.2) were prepared to study their multiferroic properties at various temperatures. Bi1 − xDyxFeO3 (x = 0–0.08) shows rhombohedral phase, ferroelectric polarization of > 18 μC/cm2, and piezoelectric d33 value of > 35 pC/N at room temperature. After the polarized ceramics were annealed at various high temperatures, the piezoelectric d33 changes suggest that ferroelectric component exists below 700 °C. There are ferroelectric phase and PZT-like anti-polar orthorhombic phase together in Bi1 − xDyxFeO3 (x = 0.11–0.17), although only ferroelectric phase contributes polarization and d33 which decreases with Dy concentration at this two-phase coexistence region. Finally, Bi1 − xDyxFeO3 (x = 0.2) transforms to non-polar orthorhombic phase according to structural and electric measurements.Highlights► Bi1 − xDyxFeO3 (x = 0–0.08) shows large polarization and d33 values. ► Ferroelectric component exists at 20–700 °C when x = 0–0.08. ► Ferroelectric phase and anti-polar orthorhombic phase coexist at x = 0.11–0.17.

Vertical one-dimensional ZnO nanorods were synthesized on Cu substrate at a low temperature of 450 °C through vapor phase transport method. The growth of nanorods should be consistent with the Stranski–Krastanov (SK) island growth mode. The field emission (FE) properties were tested, and the turn-on field of FE was about 2.3 V/μm at the current density of 10 μA/cm2. Meanwhile, the emission current densities reached 1 mA/cm2 at a bias field of 4.2 V/μm. The field enhancement factor β was estimated to be about 3200. The variation of emission current density was less than 5% during a 12-hour test under a field of 4.2 V/μm, which suggests the good FE stability of ZnO nanorods.Highlights► Vertical one-dimensional ZnO nanorods were synthesized on Cu substrate. ► ZnO nanorods and the substrate adhere well. ► Field emission current density is very stable.

Insulated Bi1−xSmxFeO3 (x=0–0.25x=0–0.25) were prepared to study their multiferroic properties at various temperatures. Bi1−xSmxFeO3 (x=0−0.12x=0−0.12) shows a rhombohedral-like phase, ferroelectric polarization of >17.8 μC/cm2, piezoelectric d33d33 value of >35 pC/N at room temperature. Bi1−xSmxFeO3 (x=0.125–0.2x=0.125–0.2) has a ferroelectric triclinic phase and an anti-polar orthorhombic phase together at room temperature, and Bi0.75Sm0.25FeO3 is mainly composed of a non-polar orthorhombic phase. After the polarized Bi1−xSmxFeO3 (x=0–0.165x=0–0.165) was annealed at various high temperatures, the d33d33 evolution supports ferroelectric component exist above 500 °C. Raman spectra suggests that the main component of Bi0.875Sm0.125FeO3 does not keep a rhombohedral ferroelectric phase above 400 °C, thus its ferroelectric traits at high temperature should be due to ferroelectric clusters embedded in orthorhombic phase.Highlights► Bi1−xSmxFeO3 (x=0–0.12x=0–0.12) shows large polarization and d33d33 values. ► Ferroelectric clusters are embedded in Bi0.875Sm0.125FeO3 above 400 °C. ► Ferroelectric phase and anti-polar orthorhombic phase coexist at x=0.125–0.2x=0.125–0.2.

Multiferroic BiFeO3 and Bi0.92Dy0.08FeO3 ceramics were prepared to study their crystal structures and piezoelectric properties. BiFeO3 exhibits rhombohedral phase below 810 °C. Although Bi0.92Dy0.08FeO3 ceramic also shows rhombohedral phase at room temperature, it allows the coexistence of rhombohedral phase and orthorhombic phase at 460–650 °C. Both samples have maximum polarizations of >21 μC/cm2 and piezoelectric d33 values of ∼37 pC/N at room temperature. Their polarized slices show the dielectric anomalies and impedance anomalies because of vibrating resonances below 500 °C, and the thickness vibration electromechanical coupling factor is ∼0.6 and ∼0.4 for BiFeO3 and Bi0.92Dy0.08FeO3, respectively. The vibrating resonances confirm piezoelectric responses. Furthermore, samples' impedance and resistance decrease fast with temperature increasing, which screens piezoelectric response above 550 °C.Highlights► Piezoelectric responses were observed at 20–500 °C. ► Ferroelectric component existed at 650 °C in Bi0.92Dy0.08FeO3. ► The impedance and the resistance were below 10,000 Ω above 440 °C.

The novel strain-driven morphotropic phase boundary (MPB) in highly strained BiFeO3 thin films is characterized by well-ordered mixed phase nanodomains (MPNs). Through scanning probe microscopy and synchrotron X-ray diffraction, eight structural variants of the MPNs are identified. Detailed polarization configurations within the MPNs are resolved using angular-dependent piezoelectric force microscopy. Guided by the obtained results, deterministic manipulation of the MPNs has been demonstrated by controlling the motion of the local probe. These findings are important for an in-depth understanding of the ultrahigh electromechanical response arising from phase transformation between competing phases, enabling future explorations on the electronic structure, magnetoelectricity, and other functionalities in this new MPB system.Keywords: BiFeO3; mixed phase nanodomains; morphotropic phase boundary; multiferroic; piezoelectric force microscopy