A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Perspective on the Development of Lead-free Piezoceramics

Potassium-sodium niobate lead-free piezoelectric materials: past, present, and future of phase boundaries.

Crystal structure and phase transitions of sodium potassium niobate perovskites

A Landau free energy expansion has been developed to describe the elastic constant variations of stishovite (SiO2) associated with the P42/mnm (rutile-type) ⇌ Pnnm (CaCl2-type) phase transition as a function of pressure. The transition appears to display classical second-order character, with an equilibrium transition pressure which is renormalized by coupling of the soft optic mode with spontaneous strain. Lattice parameter data from the literature show that the symmetry breaking strain is large, while the nonsymmetry breaking strains are small. These have been used to constrain the numerical values of the strain/order parameter coupling coefficients, which in turn have been used to constrain values for the Landau coefficients. When substituted into expressions for all the individual elastic constants, taking values for experimental and calculated values of the bare elastic constants from the literature, a clear view of the pattern of elastic constant variations is produced. Variations of P and S wave velocities derived from the calculated elastic constants for a second-order transition show a dip as the transition point is approached from high pressure and from low pressure but do not show a discontinuity. The velocity anomaly provides a signature for the presence of free silica in the lower mantle.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JB900419

High‐pressure elasticity of stishovite and the P42/mnm ⇌ Pnnm phase transition

Effect of sintering temperature on dielectric, piezoelectric and ferroelectric properties of BZT–BCT 50/50 ceramics

Pellets of ceramic Na1−xKxNbO3 (x = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared samples were measured in the frequency range from 10 KHz-1 MHz, and in the temperature range from 50–250°C for x = 0.2 and 0.5, and between 50 and 480°C for x = 0 compositions. It was observed that the dielectric constant and loss tangent decrease, and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature with increasing frequency.

/pdf/dielectric-properties-of-na1-xkxnbo3-in-orthorhombic-phase-1mq9z2fnzk.pdf

Dielectric properties of Na1-xKxNbO3 in orthorhombic phase

Dielectric properties of potassium sodium niobate mixed system

Using solid state reaction method, ceramic pellets of NaNbO 3 , Na 06 K 04 NbO 3 and Na 05 K 05 NbO 3 have been prepared Temperature and frequency dependence of dielectric constant and loss tangent of the prepared samples have been studied It has been observed that, at the transition temperature, dielectric constant peak shifts to lower temperature, and the dielectric constant and loss tangent peak heights decrease, with increasing frequency; which shows the relaxational behavior of this system

Relaxational behavior of mixed NaNbO3-KNbO3 system

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 Pellets of K 1-x Na x NbO 3 mixed system of different concentration have been prepared by solid solution reaction method. The subcell parameters & grain size have been calculated using X-ray diffraction data for mixed K 1-x Na x NbO 3 system where x is varied from 0, 20, 40, 50, 80, 100%. The variation of unitcell parameters and grain size with composition, at room temperature have been reported. Dielectric constant and loss tangent at room temperature and at different frequencies have also been reported. doi:10.4038/sljp.v2i0.176 Sri Lankan Journal of Physics, Vol.2 (2001) 13-19

/pdf/study-of-subcell-parameters-grain-size-and-dielectric-52dus1rb9g.pdf

Study of subcell parameters, grain size and dielectric properties of Potassium Sodium Niobate mixed system

/pdf/dielectric-behaviour-of-ba-x-sr-1-x-tio-3-perovskites-1ugj3nyowd.pdf

B. S. Semwal

Papers

Dielectric properties of Na1-xKxNbO3 in orthorhombic phase

Dielectric properties of potassium sodium niobate mixed system

Relaxational behavior of mixed NaNbO3-KNbO3 system

Study of subcell parameters, grain size and dielectric properties of Potassium Sodium Niobate mixed system

Dielectric Behaviour of Ba x Sr 1–x TiO 3 Perovskites