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Simultaneous action of photovoltaic effect and converse piezoelectric effect will induce the photostrictive effect. In contrast to the naturally occurring photostrictive material, the present study proposes a 0-3 photostrictive composite. The current photostrictive composite comprises of poly{4,8-bis[5-(2-ethyl-hexyl) thiophen-2-yl] benzo[1,2-b:4,5-b′] dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethyl-hexyl) carbonyl] thieno[3,4-b] thiophene-4,6-diyl} (PTB7-Th) as organic photovoltaic polymer matrix and Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-35PT) as the particulates. The current study shows that the present 0-3 photostrictive composite is a suitable alternative for the most popular lead-based photostrictive material. While evaluating all the effective elastic, dielectric, piezoelectric, and pyroelectric properties of 0-3 photostrictive composite, the effect of local fluctuations was incorporated in representative volume element (RVE) using the finite element method. A finite element formulation using a degenerated shell element is derived to simulate the actuation response of the proposed 0-3 photostrictive composite. Numerical studies have been performed on cantilever and simply supported beams. The maximum tip and center deflection of cantilever beam and simply supported beam bonded with 0-3 photostrictive patch is 9.75×10−4 mm and 1.22×10−4 mm, respectively. The maximum value of the effective piezoelectric coefficient d31eff, effective thermal expansion coefficient αeff, effective Young’s modulus E1eff, and effective pyroelectric coefficient peff of proposed 0-3 photostrictive composite are −3.81×10−13 m/V, 4.59×10−4 °C−1, 1.63×109 N/m2, and 7.57×10−5 C/m2 K, respectively, obtained at 25% volume fraction of particulates. This study opens possibilities of photostrictive coupling in composites.

Photostriction is a multiphysics phenomenon comprising of both photovoltaic effect and converse piezoelectric effect. The extensively researched photostrictive material is lead lanthanum zirconate titanate, i.e., Pb0.92La0.08(Zr0.65Ti0.35)0.98O3 (PLZT) ceramic. In contrast to the traditional approaches of improving deflection response, the current study proposes a 0–3 composite model to substantially enhance the effective material properties, which in turn significantly improves the deflection response. A computational framework based on finite element analysis is employed to 0–3 photostrictive composite of PLZT as matrix and Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-35PT) as the inclusions. The representative volume element (RVE) or unit cell technique is used to incorporate the local variation of constituent properties and to calculate photostrictive properties such as effective elastic, dielectric, piezoelectric, and pyroelectric properties. An opto-electro-thermo-mechanical finite element formulation was engaged to get the actuation response of photostrictive material bonded to cantilever and simply supported beam. The maximum deflection for cantilever beam attached to photostrictive composite patch having 25% inclusions volume fraction in 0–3 composite is found to be 38% more in comparison to pure PLZT material. It is established that the opto-electro-mechanical 0–3 composite actuators possess high potential in lightweight, compact and wireless actuation applications.

Flexoelectricity is a symmetry independent electromechanical coupling phenomenon that outperforms piezoelectricity at micro and nanoscales due to its size-dependent behavior arising from gradient terms in its constitutive relations. However, due to this gradient term flexoelectricity, to exhibit itself, requires specially designed geometry or material composition of the dielectric material. First of its kind, the present study put forward a novel strategy of achieving electric field gradient and thereby converse flexoelectricity, independent of geometry and material composition of the material. The spatial variation of the electric field is established inside the dielectric material, Ba0.67Sr0.33TiO3 (BST), by manipulating electrical boundary conditions. Three unique patterns of electrode placement are suggested to achieve this spatial variation. This varying direction of electric field gives rise to electric field gradient, the prerequisite of converse flexoelectricity. A multi-physics coupling based theoretical framework is established to solve the flexoelectric actuation by employing isogeometric analysis (IGA). Electromechanically coupled equations of flexoelectricity are solved to obtain the electric field distribution and the resulting displacements thereby. The maximum displacements of 0.2 nm and 2.36 nm are obtained with patterns I and II, respectively, while pattern III can yield up to 85 nm of maximum displacement.

Improvement in operating characteristics of piezoelectric materials, one of the most extensively used dielectric materials, is a major focus of research among materials scientists. Present work puts forward, a novel approach for achieving enhanced piezoelectricity in ferroelectric materials by manipulating electrode placement during poling. Three unique poling configurations, abbreviated as PC1, PC2, and PC3 are developed for exploiting the dependence of effective piezoelectric properties on spatially varying poling direction. Finite element method based numerical simulations are performed to evaluate the electric field distribution, poling direction, and their effect on effective piezoelectric coupling coefficients of PMN–0.35PT (Pb(Mg1/3Nb2/3)O3–0.35PbTiO3) piezoelectric ceramic. A two-phase solution process is developed to evaluate the local orientation of dipoles for each poling configuration and subsequently computing effective piezoelectric properties of the material in an average sense. Parametric studies are carried out to analyze the effect of aspect ratio R of sample and electrode to sample length ratio, r on effective piezoelectric properties. PC1 yields an increase of up to 135% in the magnitude of the transverse coupling coefficient $$({e}_{31}^{eff})$$ and an 8% increase in effective longitudinal coupling coefficient $$({e}_{33}^{eff})$$ while PC2 is observed to exhibit a maximum enhancement of 164% in the magnitude of $${e}_{31}^{eff}$$ and 11.2% in the magnitude of $${e}_{33}^{eff}$$ . PC3, presented as a special case, yields zero values of piezoelectric coefficients in an average sense but can result in a highly elevated net output for bending applications, owing to favorable spatial variation in stresses and associated piezoelectric coefficients.

Flexoelectric energy conversion, due to its universality and size dependence, is a potential candidate for applications in self-sustainable micro-electromechanical systems/nano-electromechanical systems. This study presents the performance indices for assessing flexoelectricity-driven energy conversion in micro-scale piezoelectric (non-centrosymmetric) and non-piezoelectric (centrosymmetric) dielectric materials. Electromechanical coupling coefficients for geometry selection and figures of merit for material selection for the two most common modes of operations, i.e., transverse mode as in bending of beams and longitudinal mode as in the compression of non-uniform cross section structures, are derived. An interplay of flexoelectricity and piezoelectricity in different circumstances is assessed for three different materials, namely, barium titanate (BaTiO3), Er-doped BST ceramic (Ba1-xTi0.96Sn0.04O3 + x mol. % Er), and polyvinylidene difluoride (PVDF), for transverse and longitudinal modes. In the transverse mode, BaTiO3 and BST are found to dominate at a beam thickness of 5 μm, while at 100 μm, PVDF shows substantially higher magnitudes of electromechanical coupling coefficients. A similar trend for the electromechanical coupling coefficient is observed in the longitudinal mode. PVDF has a very low magnitude of figure of merit in the transverse mode as compared to the other two materials (0.65% of BST and 0.71% of BaTiO3), while in the longitudinal mode, the figure of merit of PVDF exceeds the other two materials by a large magnitude (197 times of BST and 285 times of BaTiO3).

Various strategies to achieve superior converse flexoelectric response, qualitatively and quantitatively, in dielectric materials are presented. For the qualitative aspect, a novel approach for achieving converse flexoelectric effect independent of geometry or material composition of dielectric materials, by having modified electrical boundary conditions is presented. The theoretical investigation of the proposed methodology is presented and compared with the existing methods (functional grading and trapezoid-shaped sample). Later, the hybrid configurations of existing methods with the proposed strategy are analyzed and are found to enhance the actuation in some cases while decreasing in others, suggesting the possibility of a quantitatively superior effect. While the proposed method of varying electric field direction is established as an alternative to existing methods to induce electric field gradient, the FGM is found to exhibit up to 380% actuation of the closest non-hybrid strategy, i.e. trapezoid geometry.

In the present study, a functionally graded material (FGM) based dielectric composite is investigated for direct and converse flexoelectric effects induced due to material inhomogeneity. An Isogeometric analysis based formulation is employed to effectively capture the gradient terms appearing in the electro-elastic coupling constitutive laws of flexoelectricity. Non-uniform stresses and strains generated due to non-uniform elastic properties in the domain induce flexoelectricity inherently without any special geometric and/or boundary conditions. A two-dimensional (2D) FGM structure made by the combination of polyvinylidene fluoride (PVDF) and barium titanate (BaTiO3) is studied under mechanical and thermal loading conditions for its flexoelectric response. The induced polarization and voltage along with its dependence on grading index (n) is analyzed. Further, to extend the study to converse flexoelectricity, the mechanical response of the FG flexoelectric material under an applied electric potential is studied. Finally, the actuation of the structure by an applied electric field is studied. As high as 10% actuation of original displacement is observed for higher values of n. Effectiveness of the grading concept to induce flexoelectric response is established through numerical studies. Longitudinal and transverse modes of flexoelectricity are scrutinized and the concept of grading is proved to inherently induce the flexoelectricity in dielectrics without special geometric modifications.