•The BiFeO3 square micro-sheets were hydrothermally synthesized.•Piezo-electrochemical effect is from the product of piezoelectricity and electrochemistry.•Piezo-electrochemical mechanocatalytic decomposition ratio for Rhodamine B is ~ 95%.•Under vibration, the middle product, hydroxyl radicals, was observed.•Mechanocatalysis has potential for dye decomposition under vibration.A strong piezo-electrochemical effect is realized in hydrothermally synthesized multiferroic BiFeO3 micro-sheets via the product of the piezoelectric effect and the electrochemical redox effect. A novel mechanocatalysis originating from the piezo-electrochemical effect is designed to decompose dye wastewater under vibration condition on the basis of the following mechanism: When subjected to mechanical vibration, the BiFeO3 micro-sheets' surfaces will generate a large number of positive and negative electrical charges due to the piezoelectric effect of multiferroic materials, which further induces the chemical redox decomposition reaction in dye wastewater. A ~ 95% mechanocatalytic decomposition ratio of BiFeO3 is achieved for a Rhodamine B wastewater (~ 10 mg/L) and there is almost no decrease of mechanocatalytic performance after recycling BiFeO3 catalysts for five times. Strong oxidation middle active species, such as OH•, were also observed, which suggested the strong piezo-electrochemical coupling in BiFeO3 micro-sheets. Piezo-electrochemical mechanocatalysis of BiFeO3 micro-sheets has potential in developing a non-toxic, highly efficient and reusable technology for chemical catalysis by using environmental vibration waste energy.Download high-res image (508KB)Download full-size image

•The ZnO@TiO2 core-shell nanofibers were hydrothermally synthesized.•A mechano-/photo- bi-catalysis of ZnO@TiO2 was realized.•Bi-catalysis is superior to mechano-or photo-catalysis in dye decomposition.•ZnO@TiO2 is potential in utilizing mechanical/solar energy to degrade dye.A mechano-/photo- bi-catalyst of piezoelectric-ZnO@photoelectric-TiO2 core-shell nanofibers was hydrothermally synthesized for Methyl Orange (10 mg L−1) decomposition. The mechano-/photo- bi-catalysis in ZnO@TiO2 is superior to mechano- or photo-catalysis in decomposing Methyl Orange, which is mainly attributed to the synergy effect of the piezoelectric-ZnO core’s mechano-catalysis and the thin photoelectric TiO2 shell’s photo-catalysis. The heterostructure of the piezoelectric-ZnO@photoelectric-TiO2 core-shell interface, being helpful to reduce electron-hole pair recombination and to separate the piezoelectrically-/photoelectric ally- induced electrons and holes, may also make a great contribution to the enhanced catalysis performance. The mechano-/photo-bi-catalysis in ZnO@TiO2 core-shell nanofibers possesses the advantages of high efficiency, non-toxicity and tractability and is potential in utilizing mechanical/solar energy to deal with dye wastewater.Download high-res image (237KB)Download full-size image

•Pyroelectric ZnO nanorods were solvothermally synthesized.•Thermo-electrochemical coupling results from the pyroelectric/electrochemical product.•Decomposition ratio for Rhodamine B is ~ 98.15% under 22–62 °C cold–hot cycle excitation.•There was no decrease in thermocatalytic performance after ZnO being recycled 6 times.•Thermocatalysis of ZnO is potential in utilization of room temperature thermal energy.A strong thermo-electrochemical coupling in solvothermally-synthesized ZnO nanorods is achieved by combining pyroelectric effects and electrochemical oxidation, and is employed for room temperature thermocatalysis. Under 22–62 °C heating–cooling cycles, ZnO nanorods are shown to possess high thermocatalytic activity for Rhodamine B, resulting in ~ 98.15% decomposition. The active species are shown to be hydroxyl and superoxide radicals generated from the reaction between pyroelectrically-induced charges and the hydroxyl ions/oxygen gas in solution. After being recycled six times, the ZnO shows no decrease in thermocatalytic activity. Thermocatalysis offers a non-toxic, highly efficient, recyclable approach for utilization of thermal energy at room temperature.Download high-res image (411KB)Download full-size image

A strong pyro-catalytic dye degradation with an ultrahigh degradation efficiency (>99%) in hydrothermally synthesized pyroelectric BiFeO3 nanoparticles was achieved under a room-temperature cold–hot alternating excitation (between 27 °C to 38 °C). The pyro-catalysis originated from a combination of the pyroelectric effect and the electrochemical oxidation–reduction reaction. The intermediate products (hydroxyl radicals and superoxide radicals) of pyro-electro-catalysis were observed. Pyro-catalysis provides a highly efficient and reusable dye wastewater decomposition technology through utilizing environmental day–night temperature variation.

•The Er3+ doped (Ba1-xCax)(Sn0.06Ti0.94)O3 ceramics were sintered.•High sensitivity of photoluminescent and ferro-/piezoelectric properties on phase transition was found.•Photoluminescence indicating piezoelectric’s morphotropic phase boundary was developed.The 0.5 mol% Er3+-doped piezoelectric (Ba1-xCax)(Sn0.06Ti0.94)O3 lead-free ceramics were prepared via a conventional solid-state sintering process. The confirmed morphotropic phase boundary of this material locates at x = 0.03 through measuring x dependence on dielectric and ferro-/piezoelectric performances. It was found that photoluminescence of Er3+-doped (Ba1-xCax)(Sn0.06Ti0.94)O3 ceramics is sensitive to the structural phase transition. With the increase of x from 0.01 to 0.06, the photoluminescence peak intensity at 550 nm first increases and then decreases, giving to the optimal value at x = 0.03. The typical characteristic, photoluminescence sensitive to morphotropic phase boundary, can be used to develop a non-contact and sensitive way to indicate phase transition region of rare-earth doped lead-free piezoelectric ceramics.

●The Er3+-doped (Ba0.95Sr0.05)(Zr0.1Ti0.9)O3 ferroelectric ceramic was sintered.●Strong dependence of polarized-electric field on photoluminescence was found.●A linear relationship between photoluminescence and piezoelectric coefficient is found.●It provides a non-contact and optical way to monitor piezoelectric coefficient.In this work, a strong dependence of polarization electric field (E) on photoluminescence of Er3+-doped (Ba0.95Sr0.05)(Zr0.1Ti0.9)O3 piezoelectric ceramic is found. With the increase of E from 0 to 4.5 kV/mm, both the photoluminescence intensity at 550 nm and the piezoelectric constant d33 exhibits an increasing trend. After experiencing a polarization treatment under an electric field of >4 kV/mm, the peak intensity ratio of the poled sample to that of the unpoled sample reaches a plateau following a constant value of ~6 times enhancement. A good linear relationship between the photoluminescence and the piezoelectric coefficient is observed. The phenomenon may originate from lattice distortion induced by electric field, which lowers the local symmetry around Er3+ ions. The electric-field-induced enhancement of photoluminescence is potential in optically monitoring piezoelectric constant.

•The Er3+ doped (Ba0.97Ca0.03)(Sn0.06Ti0.94)O3 ceramic was synthesized.•The 525 nm luminescent peak is sensitive to the ferroelectric Curie transition.•It provides a noncontact and optical way to indicate the ferroelectric transition.Er3+-doped ferroelectric (Ba0.97Ca0.03)(Sn0.06Ti0.94)O3 (BCST-Er) ceramic, with a Curie temperature (Tc) of ~353 K, was prepared by a conventional solid-state reaction technique. The temperature dependence on up-conversion emissions of BCST-Er ceramic was investigated. It is experimentally observed that the maximum 525 nm luminescent emission occurred near the Tc. Consequently, this result provides a noncontact way to indicate the ferroelectric Curie phase transition.

•Stress-induced ferroelectric depolarization was experimentally observed.•A theoretical analysis was done to simulate the ferroelectric loop under stress.•The result is useful for application of ferroelectric devices in stress environment.It is experimentally and theoretically found that the uniaxial compressive stress (σ) can lead to the decrease of both the ferroelectric remanent polarization (Pr) and the coercive field (Ec) of <001>-oriented 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 crystal. With the increase of σ from 0 to −15 MPa at 50 °C, Pr decreases from 20.69 μC/cm2 to 17.30 μC/cm2 and Ec decreases from 2.19 kV/cm to 1.89 kV/cm, respectively. A numerical simulation based on a phenomenological Landau-Khalatnikov theory is used to plot the polarization hysteresis loop under σ. The result of numerical simulation agrees with the experimental observation very well. The research is useful for the application of ferroelectric devices in strain engineering.

•Photoluminescence can indicate composition of (Ba1−xCax)(Zr0.1Ti0.9)O3:Er3+.•It was attributed to the high hypersensitivity of Er3+ to the lattice symmetry.•It provides a noncontact and quick way to indicate the composition change.This paper reports that Er3+-doped (0.5 mol%) lead-free (Ba1−xCax)(Zr0.1Ti0.9)O3 dense ceramics, synthesized via a sol–gel synthesis route and a ceramic sintering process, possess excellent photoluminescence performance, which is sensitive to compositional changes. The morphotropic phase boundary (MPB) of (Ba1−xCax)(Zr0.1Ti0.9)O3 was found to be located at x=0.15 based on experimental dependence curves of dielectric and piezoelectric constants on x. The photoluminescence dependence on the compositional changes at MPB was also investigated. The study revealed that on increasing x from 0.05 to 0.30, the photoluminescence peak intensity at 550 nm first increased and then decreased, giving to an extreme value at x=0.15. The strong dependence of photoluminescence on x was attributed to the high hypersensitivity of Er3+ to lattice symmetry.