Theory of compositionally graded ferroelectrics and pyroelectricity

Marvan, M.; Chvosta, Petr; Fousek, J.

doi:10.1063/1.1940729

Cited by 20 publications

(17 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The effects of interest are intrinsic to the material and result from the macroscopic broken inversion symmetry. Further, theoretical work has also pointed out that apart from a polarization gradient, inhomogeneities in composition and strain 18 can also play a role in generating a symmetry breaking internal field. [19][20][21] In particular, flexoelectric coupling (which relates polarization and strain gradients in a material) has been recently shown to significantly affect the properties of ferroelectrics, particularly in thin films with large strain gradients due to structural relaxation via misfit dislocation formation [22][23][24] and near surfaces and interfaces.…”

Section: Introductionmentioning

confidence: 99%

Large built-in electric fields due to flexoelectricity in compositionally graded ferroelectric thin films

et al. 2013

View full text Add to dashboard Cite

TitleLarge built-in electric fields due to flexoelectricity in compositionally graded ferroelectric thin films We investigate the origin of large built-in electric fields that have been reported in compositionally graded ferroelectric thin films using PbZr 1−x Ti x O 3 (0.2 < x < 0.8) as a model system. We show that the built-in electric fields that cause a voltage offset in the hysteresis loops are dependent on strain relaxation (through misfit dislocation formation) and the accompanying polarization distribution within the material. Using a GinzburgLandau-Devonshire phenomenological formalism that includes the effects of compositional gradients, mechanical strain relaxation, and flexoelectricity, we demonstrate that the flexoelectric coupling between the out-of-plane polarization and the gradient of the epitaxial strain throughout the thickness of the film, not other inhomogeneities (i.e., composition or polarization), is directly responsible for the observed voltage offsets. This work demonstrates the importance of flexoelectricity in influencing the properties of ferroelectric thin films and provides a powerful mechanism to control their properties.

show abstract

Section: Introductionmentioning

confidence: 99%

Large built-in electric fields due to flexoelectricity in compositionally graded ferroelectric thin films

et al. 2013

View full text Add to dashboard Cite

show abstract

“…For the quantum system the pseudospin variables s z iζ are replaced with pseudospin operators s z iζ with eigenvalues ±1/2 and the tunnelling term (6) should be added to the Hamiltonian. The operator s x iζ plays the role of the tunnelling operator through the barrier and ζ is the tunnelling frequency.…”

Section: Clamped Crystalmentioning

confidence: 99%

“…Indeed, it is necessary to change the classical Landau expansion of the free energy density by adding the term, which perturbs the centrosymmetric symmetry (that means the transformation P → −P). It can be done by introducing the term γ P · gradc [5,6,11] to the volume part of the free energy density. Although the magnitude of this term can be small its influence can be important because due to this term one of the possible polarization direction is preferred.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Origin of the linear term in the pseudo-spin Hamiltonian of compositionally graded ferroelectrics

Klic

Marvan

2007

J Electroceram

Self Cite

View full text Add to dashboard Cite

This paper is devoted to the microscopic theory of compositionally graded ferroelectrics (CGF). From a simple microscopic picture of CGF we deduce the so called transverse Ising pseudo-spin model. However the Hamiltonian used in recent papers does not contain a linear term in pseudo-spins. We show that for inhomogeneous material it is necessary to modify the Ising Hamiltonian by addition of the linear term in pseudo-spins. This linear term is equivalent to introduction of an external bias field. The influence of long-range forces is discussed.

show abstract

“…The work in Ref. 15 showed that flexoelectricity plays an important role in increasing the pyroelectric property of graded ferroelectric materials and 16 investigated the large built-in electric fields in graded ferroelectric thin films due to flexoelectric coupling. In our previous work, 5 we have computationally demonstrated the possibility of designing such composites through suitable topologies, material property differences, and the selection of optimum feature sizes.…”

mentioning

confidence: 99%

Piezoelectricity above the Curie temperature? Combining flexoelectricity and functional grading to enable high-temperature electromechanical coupling

Mbarki¹,

Baccam²,

Dayal³

et al. 2014

Applied Physics Letters

View full text Add to dashboard Cite

Most technologically relevant ferroelectrics typically lose piezoelectricity above the Curie temperature. This limits their use to relatively low temperatures. In this Letter, exploiting a combination of flexoelectricity and simple functional grading, we propose a strategy for high-temperature electromechanical coupling in a standard thin film configuration. We use continuum modeling to quantitatively demonstrate the possibility of achieving apparent piezoelectric materials with large and temperature-stable electromechanical coupling across a wide temperature range that extends significantly above the Curie temperature. With Barium and Strontium Titanate, as example materials, a significant electromechanical coupling that is potentially temperature-stable up to 900 C is possible. A piezoelectric material couples electric fields with mechanical stress and deformation. It enables the conversion of stimuli and energy between electromagnetism and mechanics, and has important applications that range from energy harvesting to artificial muscles.1 Perovskites such as Barium Titanate (BaTiO 3 ) and Lead Titanate (PbTiO 3 ) are two widely used materials that exhibit a fairly high electromechanical coupling.2-4 The piezoelectricity in these materials, which are also ferroelectric, are driven by an asymmetric distribution of charges in the atomic unit cell. Above the Curie temperature (T c ), the crystal structure transforms to a centrosymmetric state, and both ferroelectricity and piezoelectricity disappear. For example, at T c ¼ 120 C in BaTiO 3 , it transforms from a non-centrosymmetric tetragonal crystal to a centrosymmetric cubic crystal. The loss of piezoelectricity at such (relatively) low temperatures hinders their potential application to areas ranging from hypersonics to oil extraction, which require high-temperature energy harvesting, harsh environment sensing, and actuation, among others.We exploit flexoelectricity as the first element of our strategy to go beyond this limitation. Flexoelectricity denotes the coupling between polarization and strain gradients; this is in contrast to piezoelectricity that relates polarization to strains. The difference between piezoelectricity and flexoelectricity can be readily observed from the following equation:where, P i is the electric polarization, S jk is the strain tensor, e ijk is the third order piezoelectric tensor, and f ijkl is the fourth order flexoelectric tensor. Flexoelectricity is a property that is displayed by all dielectrics to some degree. Thus, in a centrosymmetric material, where the piezoelectric tensor e vanishes, non-uniform strains can still induce a polarization. Flexoelectricity is mediated through the fourth-order tensor f, and unlike e, symmetry principles permit its existence in all types of crystal structure and not just non-centrosymmetric crystals. For instance, while BaTiO 3 will cease to be piezoelectric above T c ¼ 120 C, it can still display flexoelectricity. Flexoelectricity has recently received much attention, e.g., it suggests tantali...

show abstract

Theory of compositionally graded ferroelectrics and pyroelectricity

Cited by 20 publications

References 16 publications

Large built-in electric fields due to flexoelectricity in compositionally graded ferroelectric thin films

Large built-in electric fields due to flexoelectricity in compositionally graded ferroelectric thin films

Origin of the linear term in the pseudo-spin Hamiltonian of compositionally graded ferroelectrics

Piezoelectricity above the Curie temperature? Combining flexoelectricity and functional grading to enable high-temperature electromechanical coupling

Contact Info

Product

Resources

About