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Piezoelectricity is one of the important functional properties inherent to many biomaterials. It stems from the non-centrosymmetric crystal structure of most biopolymers including proteins, polysaccharides, and lipids. Understanding the relationship between the generated electric field and applied mechanical stress has become the main motivation to studying piezoelectricity in biological systems and artificial biomaterials at the nanoscale. In this work, we present a review of the piezoelectric and ferroelectric properties of several molecular systems and nanomaterials revealed by Piezoresponse Force Microscopy (PFM) and compare the results with molecular modeling and computer simulations. Experimentally observed by PFM and calculated dielectric, piezoelectric, and ferroelectric properties of these materials are analyzed in the context of their possible role in functionality of biological systems. [ABSTRACT FROM AUTHOR]

Piezoresponse Force Microscopy (PFM) is used to characterize the nanoscale electromechanical properties of centrosymmetric CaCu3Ti4O12 ceramics with giant dielectric constant. Clear PFM contrast both in vertical (out-of-plane) and lateral (in-plane) modes is observed on the ceramic surface with varying magnitude and polarization direction depending on the grain crystalline orientation. Lateral signal changes its sign upon 180° rotation of the sample thus ruling out spurious electrostatic contribution and confirming piezoelectric nature of the effect. Piezoresponse could be locally reversed by suitable electrical bias (local poling) and induced polarization was quite stable showing long-time relaxation (∼3 hrs). The electromechanical contrast in unpoled ceramics is attributed to the surface flexoelectric effect (strain gradient induced polarization) while piezoresponse hysteresis and ferroelectric-like behavior are discussed in terms of structural instabilities due to Ti off-center displacements and structural defects in this material. [ABSTRACT FROM AUTHOR]

Ti-rich PbZr1-xTixO3 (x = 0.65, PZT65) single crystals with the dimensions of 1 × 1 × 0.2 mm3 were grown by the self-flux method. Micron-sized ferroelectric domains were observed and characterized via piezoresponse force microscopy (PFM) and switching spectroscopy PFM. Both out-of-plane and in-plane components of polarization were obtained by detecting vertical and lateral vibrations of the PFM cantilever. The piezoresponse image examination revealed a clear lamellar domain structure due to apparent twinning and the formation of 90° domains. A negative self-polarization was observed in the studied crystals leading to the asymmetry of piezoresponse hysteresis loops and the polarization imprint. The polarization switching mechanism under the external electric field applied via a PFM tip was investigated. The 90° domain wall width was determined from the local PFM measurements and tentatively attributed to the oblique domain walls and chemical disorder. The time-dependent PFM imaging revealed a slow polarization relaxation process with a characteristic time of about 200 min. [ABSTRACT FROM AUTHOR]

We used piezoresponse force microscopy (PFM) to study the dc bias field-induced domain structure of the (001) oriented single crystals of 0.77PbMg1/3Nb2/3O3-0.23PbSc1/2Nb1/2O3 relaxor. In the as-grown state, no polarization contrast was observed due to the average cubic symmetry of the crystal. Upon application of a dc bias applied via a PFM tip, a stable complex domain pattern, corresponding to a hedgehog-type topological defect, appeared on the surface of the crystal. The shape of these domains depended on the magnitude of the field. If the field was below a threshold, the domains possessed a cylindrical form. Above the threshold, the border between domains became close to a straight line. At high biases and large separation between the pulses, the development of the domains obeyed an avalanche-type dynamics. [ABSTRACT FROM AUTHOR]

Direct measurements of the motion of domain walls in disordered ferroelectrics provide important information on their interaction with defects, which is crucial for the functioning of various ferroelectric devices such as high-K capacitors and ferroelectric-based memories. In this work, we report on the results of the nanoscale measurements of domain-wall velocity and static domain-wall roughness in disordered (Pb,La)(Zr,Ti)O3 (PLZT) ceramics prepared by hot press sintering. Relaxation of domain walls to their equilibrium configurations at short length scales yields the apparent roughness exponent ζ ≈ 0.67 in PLZT 9.5/65/35. At the same time, the dynamical exponent μ was found to be about 0.25 from the independent measurements of domain-wall creep under local application of electric field. An analysis of these two values points to the effective dimensionality deff = 1 for the domain walls in PLZT with high La content. This result is confirmed by the layer-by-layer polishing followed by the imaging of an artificially created domain. The origin of disorder and its dependence on La concentration in PLZT solid solutions are discussed. [ABSTRACT FROM AUTHOR]

Nanostructured aminoacid glycine and nucleobase thymine are very important for various biomedical applications. Experimentally, these structures demonstrate piezoelectric and polar properties. But the value of polarization and its switching behavior are not clear yet. In this work, computational modeling of glycine polymorphic phases (α and β) and thymine nanostructures was performed using a combined method with LDA first principle calculations of atomic optimized crystal structures in AIMPRO code on Linux cluster combined with molecular semi-empirical PM3 calculations by HyperChem 8.0. The developed molecular model and calculated parameters are compared with recent measurements using piezoresponse force microscopy (PFM) at the nanoscale. [ABSTRACT FROM PUBLISHER]

Ferroelectricity and piezoelectricity are two of the common ferroelectric material properties, which have widespread observations in many biological systems, and these are referred to as biopiezoelectricity and bioferroelectricity. This paper presents a short overview of the main issues of piezoelectricity and ferroelectricity, their manifestation in organic, biological, and molecular systems. As a showcase of novel biopiezomaterials, the investigation of diphenylalanine (FF) peptide nanotubes (PNTs) is described by computational molecular modeling, as well by experimental AFM/PFM measurements. FF PNTs present a unique class of self-assembled functional biomaterials, owing to their wide range of useful properties, including nanostructural piezoelectric and ferroelectric properties. [ABSTRACT FROM AUTHOR]

In this work, the nanoscale electromechanical properties of Pb-based perovskites that are currently the main candidates for piezoelectric applications are investigated by Piezoresponse Force Microscopy (PFM). Local response is compared with that studied via conventional technique. The effect of local polarization switching by mechanical force is demonstrated. This effect may limit the functionality of the films in piezoelectric applications. Local piezoelectric nonlinearity, as well as the nanoscale degradation are also studied by PFM. These measurements demonstrate that the defects may act as pinning centers for domain walls and thus influence nanoscale properties. Finally, local properties of ferroelectric relaxors are presented. [ABSTRACT FROM AUTHOR]

Thermodynamic approach of ferroelectrics is reconsidered in recourse to thermal activated nature of polarization switching under arbitrary driving voltage. This analysis heavy relies on transformation of the problem to imaginary time Schrödinger equation and its integration by means adopted from pure quantum problems. It turns out that this nonadiabatic treatment reveals non-equilibrium properties directly relevant to reconstruction of local polarization from contact mode atomic force microscope measurements. [ABSTRACT FROM AUTHOR]

X-ray diffraction (XRD) and Raman scattering in sol–gel derived Pb1−xCaxTiO3 (PCT) thin films are studied as a function of Ca content x. It is found that Ca2+ addition to PbTiO3 films results in a gradual decrease of tetragonality of the perovskite lattice accompanied with a considerable modification of the Raman spectra. A significant difference in Raman spectra of PCT films and available reference data for single crystals (x=0) is explained in terms of the large internal stress, small grain size, and structural disorder produced by Ca2+ substitution. It is found that the shift of the frequency of ferroelectric soft mode correlates well with the variation of tetragonality for x≤xc=0.4. The concentration dependence of the shift is strongly non-linear being qualitatively different from that observed earlier in other A-site doped lead titanate-based systems. According to XRD data, the averaged crystal structure for xc≈0.4 appears as pseudo-cubic, while Raman scattering revealed short-range order tetragonal distortion. The structural characteristics of PCT films are linked to their electromechanical properties measured earlier by interferometric technique. [Copyright &y& Elsevier]

The domain structure of high-quality SrBi2Ta2O9 (SBT) single crystals is investigated by x-ray diffraction and piezoelectric force microscopy. Both ferroelectric 180° domains and ferroelastic 90° domains (twins) are revealed at room temperature. Remarkably, coexisting domains of two types form a well-defined “herringbone” structure with mostly flat 90° walls. Formation of the observed complex domain pattern is attributed to a two-stage process associated with the presence of separate ferroelastic and ferroelectric phase transitions in SBT. [ABSTRACT FROM AUTHOR]