The Piezoelectric Medium and Its Electromechanical Properties

Abstract

An effect that links a mechanical action (mechanical stress or strain) with an electric response (electric field, displacement or polarisation) is the piezoelectric effect or, more exactly, the direct piezoelectric effect [1]. This effect was first studied by brothers P. Curie and J. Curie in experimental work (1880) on the behaviour of quartz single crystals (SCs) subjected to an external mechanical stress. At a later date, the converse piezoelectric effect was revealed in acentric dielectric SCs wherein an external electric field generated a mechanical response, i.e., a stress or strain of the sample [2,3]; similar to electrostriction of dielectrics [3,4]. The piezoelectric effect follows a linear relationship between electric and mechanical variables and originates from the displacement of ions of an acentric SC under an applied electric field [1][2][3][4]. This relationship means that there is change in the sign of the effect when the direction of the external electric field is switched in the piezo-active medium, unlike electrostriction which follows a quadratic effect [3,4] and does not undergo switching with the electric field. Despite the linear character, the piezoelectric response of a SC sample is often intricate owing to various interconnections between the piezoelectric and other properties such as the elastic, dielectric (including pyro-and ferroelectric) and thermal properties [3]. The piezoelectric response of poled ferroelectric ceramic (FC) and composite samples are even more complicated in comparison to ferroelectric SCs due to microstructural, domain, orientation, intrinsic and extrinsic contributions, etc. [5][6][7][8][9][10][11].Piezoelectricity was initially discovered as a physical phenomenon and has led to a range of new adapted materials and technologies in the past 130 years. It was a long and sometimes difficult path to improve the initially minor effect to a point where is was a real and even superior competitor to the electro-dynamic magnetic principal, which for a long time was the only effective way to transform electrical energy or signals into mechanical ones or vice versa [11]. In the history of piezoelectric materials there is the remarkable era concerned with the perovskite-type FC of BaTiO 3 . After discovering the ferroelectric properties and ability to orient the ferroelectric domains within grains (or crystallites) of FC BaTiO 3 in an external electric field, a new way of producing the highly-effective piezoelectric materials was opened in the 1940s.

Advantages and challenges of relaxor-PbTiO3 ferroelectric crystals for electroacoustic transducers – A review

“…Other engineered connectivities, such as parallel-connected 2-2 composites, which are stacks of piezoelectric ceramic sheets separated by passive polymer layers, have also been investigated [97–99,101,105]. Recently, 2-2 lamellar composites consisted of relaxor-PT single crystals have been theoretically studied, giving a promising FOM of 16 pm 2 /N for a crystal volume of 25 % [107–109]. The 2-2 composite takes advantage of the strong anisotropic behavior of [011] C poled single crystals, with macroscopic mm2 symmetry, in which the d 33 and d 31 are both positive while d 32 is negative.…”

Understanding the peculiarities of the piezoelectric effect in macro-porous BaTiO3

“…Such a composite is described by 3–0 connectivity in terms of work. [3,12,13] The effective electromechanical (i.e. elastic, piezoelectric and dielectric) properties of the porous 3–0 composite are determined in the matrix form by using the dilute approach,[5] and in this case any interaction between the inclusions can be neglected.…”

2-2 composites based on [011]-poled relaxor-ferroelectric single crystals: from the piezoelectric anisotropy to the hydrostatic response

“…curves 3 and 4 in Fig. 4, c), and max( [3]. The aforementioned correlation may be a result of the strong influence of the piezoelectric properties of the composite on its hydrostatic electromechanical coupling factor from Eq.…”

“…1). The main crystallographic axes X, Y, and Z of each single-domain SC layer in the initial state are parallel to the co-ordinate axes OX j as follows: X || OX 1 , Y || OX 2 and Z || OX 3 . This means that rotation angles in the initial state obey the conditions α = 0° (inset 1 in Fig.…”

“…from Eqs (3). and(4), respectively, characterise the effectiveness of the conversion of mechanical energy into electric energy and vice versa.…”