Jiří Erhart

Fundamentals of Piezoelectric Sensorics

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Scanning force microscopy of domain structures in Pb(Zn1/3Nb2/3)O3-8% PbTiO3 and Pb(Mg1/3Nb2/3)O3-29% PbTiO3

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Direct and ultrasonic measurements of macroscopic piezoelectricity in sintered hydroxyapatite

Domain structures of unpoled as well as poled (along [001]- and [110]-direction) Pb(Zn1/3Nb2/3)O3 (PZN)-8% PbTiO3 (PT) and Pb(Mg1/3Nb2/3)O3 (PMN)-29% PT single crystals have been investigated by scanning force microscopy (SFM) in the piezoresponse mode, at room temperature. Antiparallel domain structures have been detected mostly in unpoled crystals of both materials, with a fingerprint pattern in (001)-oriented PZN-8% PT crystal. The ferroelastic domain wall has been identified in poled (110)-oriented PZN-8% PT crystal. “Writing” of ferroelectric domains has been performed by applying a dc voltage to the SFM tip. Local re-poling has been observed for all unpoled as well as for poled (001)-oriented crystals at the voltage ±60 V. Local electrical switching was successful in poled (110)-oriented PMN-29% PT at higher voltage (±120 V) but was not successful in poled (110)-oriented PZN-8% PT crystal. Domain-engineered crystals poled in [110]-direction seem to exhibit more stable (in the sense of local re-polin...

Effective material properties in twinned ferroelectric crystals

Macroscopic piezoelectricity in hydroxyapatite (HA) ceramic was measured by a direct quasistatic method and an ultrasonic interference technique. The effective symmetry of polycrystalline aggregate was established and a detailed theoretical analysis was carried out to determine by these two methods the shear piezoelectric coefficient, d14, of HA. Piezoelectric nature of HA was proved qualitatively although a specific quantitative value for the d14 coefficient could not be established. Ultrasound method was also employed to anisotropic elastic constants, which agreed well with those measured from the first principles.

Pyroelectric surface charge in hydroxyapatite ceramics

Without external fields, ferroelectric materials will have multidomain configuration in the ferroelectric state. Detailed analysis found that twinning may not be treated as random since the number of orientations for the domain walls are limited in a given symmetry change during a ferroelectric phase transition. In each finite region of a large crystal or in small crystallites, a particular set of twins is favored under certain boundary conditions, which consists of only two of the low temperature variants. Statistic models of random distribution of domains do not apply for calculating the physical properties of such twin structures. However, one could derive the two domain twin properties by using the constitutive equations and appropriate mechanical boundary considerations. This paper presents a theoretical analysis on such a two-domain twin system, including its global symmetry and effective material properties resulting from different twinning configurations. Numerical results are derived for LiNbO3 a...

Domain wall orientations in ferroelastics and ferroelectrics

Surface charge of pyroelectric nature is measured in poled hydroxyapatite ceramics. The average pyroelectric constant can range from 0.1 to 40 nC cm−2 K−1 at temperatures of 300–500 °C, while at 27–60 °C the value ranges from 15 to 64 nC cm−2 K−1. The higher temperature values are comparable to conventional pyroelectric ceramics such as LiTaO3 or PZT. The lower temperature values are four orders higher than those observed in bone and tendon.

What is really measured on a d33-meter?

This paper concerns the problem of orientations of domain walls in ferroelastic and/or ferroelectric single crystals. They are specified on the basis of elastic compatibility of the neighbouring domains. Results are presented in form of tables, which make it possible to find spontaneous tensors (i.e. strain and polarization) for each domain state in any ferroelastic and/or ferroelectric species. Domain wall orientations are listed in tables for all combinations of domain states. For each domain wall orientation, their charge or neutrality is indicated. Results are summarized in comprehensive table including numbers of possible domain states, domain wall types (W ∞, W f , S) and their charge or neutrality. Domain pairs with non-permissible domain walls (R case) are also specified.This paper concerns the problem of orientations of domain walls in ferroelastic and/or ferroelectric single crystals. They are specified on the basis of elastic compatibility of the neighbouring domains. Results are presented in form of tables, which make it possible to find spontaneous tensors (i.e. strain and polarization) for each domain state in any ferroelastic and/or ferroelectric species. Domain wall orientations are listed in tables for all combinations of domain states. For each domain wall orientation, their charge or neutrality is indicated. Results are summarized in comprehensive table including numbers of possible domain states, domain wall types (W ∞, W f , S) and their charge or neutrality. Domain pairs with non-permissible domain walls (R case) are also specified.

Domain Engineered Piezoelectric Ceramic Transformers

Abstract Mechanical boundary conditions of PZT sample are not well defined in the measurement process on a d33-meter due to the misfit in size or shape of the jaws and of the sample. Result of such d33 measurement is usually an effective value d 33 eff . Mechanical stress/strain conditions are simulated for PZT discs/cylinders in a d33-meter by the finite element method (ANSYS® software) and an effective d 33 eff is calculated and compared to the original input d33 value as well as to the values measured on a d33-meter (type ZJ-3C). Relative d 33 eff d 33 value seems to be more sensitive to the disc aspect ratio than to the PZT material type tested. Although such strong dependence on the aspect ratio has been found in simulations, it is not correlated with experiments. Coefficient d 33 eff is not significantly sensitive to the position of a d33-meter metallic jaws with respect to the disc center.

Elastic Properties of Crystals

Piezoelectric transformers (PTs) based on thin ceramics disc with the double “ring-dot” electrode design are studied on the domain engineered ceramics disc. Various possibilities of the domain volume distributions are experimentally prepared and the problems of non-homogeneous poling are discussed. Parameters of PTs such as transformation ratio and efficiency are measured as a function of frequency, resistive load and electrode geometry. The best transformation ratio and efficiency parameters were found for the homogeneously poled PT samples. Domain engineered poling direction distribution with alternating oppositely poled segments are the best among the non-homogeneously poled PTs, although the parameters are not better than for the homogeneously poled PTs.

Bulk piezoelectric ceramic transformers

The objective of present day physics is to describe and explain the properties of solid materials, in particular of crystals, on the basis of their atomic structure. In this chapter we will not pursue this aim. The treatment of matter here will be confined to the continuum model. In this model a body consists of a compact continuous set of material points. The boundary of this set of points is called the surface of the body. Frequently it is convenient to consider a body as a material element cut out of the surrounding continuum. The surface then separates the body under consideration from its surroundings.