Ferroelectric hafnium zirconium oxide (HZO) thin films show significant promise for applications in ferroelectric random-access memory, ferroelectric field-effect transistors, and ferroelectric tunneling junctions. However, there are shortcomings in understanding ferroelectric...

BiFeO3 (BFO), a room temperature multiferroic, undergoes a series of structural transformations under varying strain conditions by utilizing appropriate substrates for a specific strain condition. In this study, epitaxial thin films of BFO were grown on La0.7Sr0.3MnO3±δ (LSMO), a strain tuning layer on LaAlO3[LAO (001)] substrates, using pulsed laser ablation. LSMO layers of varying thicknesses from 2 nm to 20 nm were grown followed by a BFO layer of a fixed thickness (20 nm). A strained layer of ∼2 nm thick LSMO stabilizes the tetragonal like phase of BFO. Increasing the thickness of the LSMO layer to 10 nm results in a mixed phase with rhombohedral (R) and tetragonal (T) domains, and a further increment of the LSMO layer thickness to 20 nm stabilizes the rhombohedral phase of BFO. The tetragonal phase with weak monoclinic distortion possessed 180° domains with dominant out-of-plane polarization components. However, the mixed phase (R + T) possessed various plausible polarization components in both out-of-plane and in-plane directions. Further, a thermodynamically consistent model based on the phase field approach was implemented to investigate the role of strain on the formation of domain patterns with various polarization components and piezoelectric coefficients. The simulated domain structure exhibited a similar transformation on the dominant polarization components as observed in experiments across different phases of BFO. Our simulations show that the elastic constraint along the z-direction enhances the tetragonality of BFO. The piezoelectric (d33) coefficient was found to be ∼46 pm/V for the 20 nm mixed phase BFO, which was nearly a 200% increment compared to the single phase BFO thin films on LAO.

Polyvinylidenefluoride (PVDF) a semicrystalline pieozoelectric polymer was synthesized with varying process conditions and its ferroelectric domain orientations were studied using piezoresponse force microscope (PFM). PVDF thin films fabricated using tape casting technique with precursor solutions of varying viscosities reveal that the polarization components transform from a dominant planar to an out‐of‐plane configuration with increase in viscosity. Interestingly the planar components possessed a head to head or tail to tail kind of paired domains separated by a distance of ~ 380‐400 nm. Electrostatic energy minimization of an electrically inhomogeneous system containing similar domain arrangements as the experiments shows that the head to head and tail to tail arrangements with a minimum separation distance are more favorable than head to tail arrangements of domains. With increment of applied field, the domains grew in size and shape indicating amorphous to crystalline transformation of PVDF films. Such transformation was evident from X‐ray diffraction studies performed in‐situ in the presence of an applied electric field.

We present a thermodynamically consistent phase-field model describing the free energy of perovskite-based BCT-BZT solid solution containing an intermediate morphotropic phase boundaries. The Landau coefficients are derived as functions of composition of zirconium. The electrostrictive and elastic constants are appropriately chosen from experimental findings. The resulting Landau free energy is constructed to describe the stable polarization states as a function of composition. The evolution of the polarization order parameters at a particular composition is described by a set of time-dependent Ginzburg-Landau (TDGL) equations. Additionally, we solve Poisson's equation and mechanical equilibrium equation to account for the ferroelectric/ferroelastic interactions. We have performed two dimensional and three-dimensional simulations with appropriate electrical boundary conditions to study the effect of external electric field on domain dynamics in BCT-BZT system at the equimolar composition.

Application of lattice strain via epitaxial growth of perovskite oxide ferroelectric and multiferroic films and superlattices on compliant lattice-mismatched substrates is an important strain-engineering technique to tune their dielectric and piezoelectric properties. Both first principles calculations of electronic structures and phenomenological models based on Ginzburg–Landau–Devonshire (GLD) theory have been used to predict the effect of strain-tuning on structure-property relations in ferroics. In this chapter, we focus on the application of phenomenological GLD models for predicting phase transitions and domain structure evolution in strained ferroelectrics. First we describe key crystallographic and thermodynamic aspects of the mean-field GLD theory of ferroics. Next we describe phase-field models of ferroelectrics. GLD theory forms the basis of phase-field models of domain structure evolution of ferroelectrics. Phase-field models assume a diffuse interface between coexisting phases and avoid explicit tracking of interface. Thus, complex domain morphology in ferroics during paraelectric to ferroelectric phase transition can be conveniently simulated using these models. Here we provide the recipe to performphase-field simulations of strained ferroics to predict their structure-property relations as a function of external electromechanical loading. We also provide a few examples of phase-field implementation and conclude by summarizing the future scope of these models.