Wavelength dependence of photoinduced deformation in BiFeO3

Abstract

Optomechanical effects in polar solids result from the combination of two main processes, electric field-induced strain and photon-induced voltages. Whereas the former depends on the electrostrictive ability of the sample to convert electric energy into mechanical energy, the latter is caused by the capacity of photons with appropriate energy to generate charges and, therefore, can depend on wavelength. We report here on mechanical deformation of BiFeO 3 and its response time to discrete wavelengths of incident light ranging from 365 to 940 nm. The mechanical response of BiFeO 3 is found to have two maxima in near-UV and green spectral wavelength regions. DOI: 10.1103/PhysRevB.85.092301 PACS number(s): 78.20.hb, 75.85.+t, 78.20.nc Cross-functional materials, where structure, charge, and magnetism are strongly interrelated, present high interest opportunities to realize new functionalities. In particular, photoelasticity in electrically polar materials is an extraordinary property with valuable remote light-controlled applications. [1][2][3] Due to the spontaneous polarization in polar dielectrics, light-generated charges distribute along the internal electricfield direction, thus changing the total electric field, and can cause sample deformation via the electrostrictive effect. Although some practical devices have been developed, the best response time with typical values of tens of seconds 4 must be improved. In that respect, our recent report on photoelastic effect in BiFeO 3 (BFO) with a fast response time may boost this research direction.5 Moreover, the observed magnetic field dependence can offer additional functionality in future photoelastic-multiferroic devices where strain, magnetization, and polarization can potentially be changed simultaneously by light as well as applied magnetic and electric fields. The BFO is a well-documented magnetic and ferroelectric compound in which both properties have been investigated rather extensively.6 Very interesting recent reports on optical properties in BFO include magnetochromism 7 and photovoltaic effects. 8,9 In this Brief Report, we investigate the wavelength dependence of the photoinduced strain in BFO single crystal for the purpose of finding an optimal cross-operational energy window of this intriguing property. Such measurements can also provide an independent indirect insight into the optical sensitivity of this extraordinary room temperature multiferroic compound.A BFO single crystal with thickness of 90 μm and lateral dimensions in the mm scale, shown on Fig. 1, was used for this study. The sample was selected using polarized light with an optical microscope revealing its single ferroelectric domain state with its spontaneous ferroelectric polarization along the [111] direction in the pseudocubic lattice description.Side 1 of the crystal is flat and reflective, allowing an easy verification of the sample ferroelectric state by polarized light in reflection mode, while side 2 exhibits a significant light absorption and indicates directions of crystal...

Electronic Origin of Ultrafast Photoinduced Strain inBiFeO3

“…Charge separation during the photovoltaic response in turn influences degrees of freedom conventionally associated with ferroelectricity: the magnitude of the spontaneous polarization and the electromechanical distortion of the lattice. As a result of these observations, photoinduced structural changes in ferroelectrics [7] and multiferroics [8,9] have been described as arising from the excitation of charge carriers. However, the timescales and mechanisms of processes that begin with the optical excitation and result in the subsequent structural distortion are largely unknown.…”

Photostriction in Ferroelectrics from Density Functional Theory

“…The photostriction phenomenon opens new perspectives for combining several functionalities in future generations of remote switchable devices and is promising for the realization of light-induced actuators 5 . It has been recently observed in BFO under visible light 6,7 . A giant shear strain generated by femtoseconds laser pulses was also reported 8,9 , and time-resolved synchrotron diffraction reported a shift of the Bragg peak on a picosecond time scale in both bismuth ferrite 10 and lead titanate 11 .…”

“…It may also either arise from a slight underestimation of the piezoelectric and/or dielectric coefficients given in Ref. 39 for the ground state of BFO, or from the fact that these coefficients, as well as the Born effective charges we used to estimate the polarization, can also technically vary when free carriers are present 7 . These latter effects may also explain why the inverse piezoelectric scenario is estimated to yield a change in lattice constant that is three times larger than what is observed from the raw ∆SCF data for the "Direct VBM" transition, as further indicated by Fig.2a -especially, when realizing that the "Direct VBM" transition, unlike the "Indirect VBM-CBM" and "Direct CBM" cases, involves a conduction state of much higher energy than the CBM state.…”

Strain modulated transient photostriction in La and Nb codoped multiferroic BiFeO3 thin films

“…17 Coupling of light with mechanical degrees of freedom in BFO was reported by Kundys et al, the light-induced wavelength dependent size change of BFO single crystal can be understood from photostriction effect, a superposition of photovoltaic effect and electrostrictive effect. 14,15 Although the photostriction effect has been found in BFO single crystal at room temperature, it remains intensive investigation aiming to understand the dynamical photostriction effect. We would like to mention that the La and Nb codoped BFO film shows a much higher electrical polarization than that of intrinsic BFO film, 18 and therefore the enhanced photostriction effect in doped BFO is expected.…”

“…4,5 In recent years, more and more attention have been focused on the linear, 6,7 nonlinear optical properties, 8,9 and the photo-induced effects in multiferroic BFO. [10][11][12][13][14][15] Noteworthy, photo-induced effects can be coupled to functional properties, such as ferroelectricity, ferromagnetism, and ferroelasticity of BFO. For example, when illuminated by ultraviolet light in an open circuit, the magnitude of the photovoltage was found to be proportional to the crystal length along the electric polarization direction.…”