Ferroelectric, dielectric and piezoelectric properties of ferroelectric thin films and ceramics are reviewed with the aim of providing an insight into different processes which may affect the behaviour of ferroelectric devices, such as ferroelectric memories and micro-electro-mechanical systems. Taking into consideration recent advances in this field, topics such as polarization switching, polarization fatigue, effects of defects, depletion layers, and depolarization fields on hysteresis loop behaviour, and contributions of domain-wall displacement to dielectric and piezoelectric properties are discussed. An introduction into dielectric, pyroelectric, piezoelectric and elastic properties of ferroelectric materials, symmetry considerations, coupling of electro-mechanical and thermal properties, and definitions of relevant ferroelectric phenomena are provided.

https://iopscience.iop.org/article/10.1088/0034-4885/61/9/002/pdf

Ferroelectric, dielectric and piezoelectric properties of ferroelectric thin films and ceramics

Recent progress in voltage control of magnetism: Materials, mechanisms, and performance

Voltage control of magnetism (VCM) is attracting increasing interest and exciting significant research activity driven by its profound physics and enormous potential for application. This review article aims to provide a comprehensive review of recent progress in VCM in different thin films. We first present a brief summary of the modulation of magnetism by electric fields and describe its discovery, development, classification, mechanism, and potential applications. In the second part, we focus on the classification of VCM from the viewpoint of materials, where both the magnetic medium and dielectric gating materials, and their influences on magnetic modulation efficiency are systematically described. In the third part, the nature of VCM is discussed in detail, including the conventional mechanisms of charge, strain, and exchange coupling at the interfaces of heterostructures, as well as the emergent models of orbital reconstruction and electrochemical effect. The fourth part mainly illustrates the typical performance characteristics of VCM, and discusses, in particular, its promising application for reducing power consumption and realizing high-density memory in several device configurations. The present review concludes with a discussion of the challenges and future prospects of VCM, which will inspire more in-depth research and advance the practical applications of this field.

Halide perovskite (HaP) semiconductors are revolutionizing photovoltaic (PV) solar energy conversion by showing remarkable performance of solar cells made with HaPs, especially tetragonal methylammonium lead triiodide (MAPbI3). In particular, the low voltage loss of these cells implies a remarkably low recombination rate of photogenerated carriers. It was suggested that low recombination can be due to the spatial separation of electrons and holes, a possibility if MAPbI3 is a semiconducting ferroelectric, which, however, requires clear experimental evidence. As a first step, we show that, in operando, MAPbI3 (unlike MAPbBr3) is pyroelectric, which implies it can be ferroelectric. The next step, proving it is (not) ferroelectric, is challenging, because of the material's relatively high electrical conductance (a consequence of an optical band gap suitable for PV conversion) and low stability under high applied bias voltage. This excludes normal measurements of a ferroelectric hysteresis loop, to prove ferroelectricity's hallmark switchable polarization. By adopting an approach suitable for electrically leaky materials as MAPbI3, we show here ferroelectric hysteresis from well-characterized single crystals at low temperature (still within the tetragonal phase, which is stable at room temperature). By chemical etching, we also can image the structural fingerprint for ferroelectricity, polar domains, periodically stacked along the polar axis of the crystal, which, as predicted by theory, scale with the overall crystal size. We also succeeded in detecting clear second harmonic generation, direct evidence for the material's noncentrosymmetry. We note that the material's ferroelectric nature, can, but need not be important in a PV cell at room temperature.

https://www.pnas.org/content/pnas/114/28/E5504.full.pdf

Tetragonal CH3NH3PbI3 is ferroelectric

The temperature sensitivity of enhanced piezoelectricity in (K,Na)NbO3 perovskite-based lead-free piezoelectrics is one of the technical bottlenecks impeding practical applications. This work found a recipe that possesses a piezoelectric strain coefficient d33* as high as 600 pm V−1 over a wide temperature range up to 100 °C, which is additionally insensitive against the frequency of an applied electrical field. Electrical property measurement and nanostructure observation revealed that the high performance combining high piezoelectricity and excellent stability benefits from a diffused phase transition (DPT), which is closely associated with the transition from ferroelectric to relaxor behavior induced by the local structural disorder due to the complicated compositional modification. The high-resolution transmission electron microscopy images of Moire fringes imply the existence of polar nanoregions (PNRs) that are responsible for the relaxor-like electrical behavior in the present materials. The findings and understanding obtained in this work should be valuable for pushing lead-free piezoelectric ceramics towards practical applications.

High-performance lead-free piezoelectrics with local structural heterogeneity

Bias (dc electric field) dependence of the dielectric constant of ferroelectric ceramics of the Pb(Zr,Ti)O3 type has been investigated. Measurements were carried out at various temperatures in the ferroelectric phase and at several frequencies between 1 kHz and 1 MHz. The bias characteristics of the dielectric constant show a temperature‐dependent asymmetry in the electric field direction. A model in which the coercive fields of the 180° and 90° domains are distributed around some average value is considered. The total dielectric constant of the material is calculated by considering the contributions of each type of domain, taking into account the difference between the differential and incremental dielectric constants. This model explains the dependence of dielectric constant on electric field. A comparison of the calculated and experimental results is presented.

Electric field dependence of the dielectric constant of PZT ferroelectric ceramics

The electric field dependence of the dielectric constant and loss of PZT perovskite-type ceramics have been investigated. Measurements were performed at frequencies of 1, 10 and 100 kHz, and 1 MHz, at several temperatures below the Curie temperature. The bias characteristics of the dielectric constant have two peaks, related to the 180° domain reversal and the 90° domain rotations, and show a temperaturedependent asymmetry in the electric field direction. A dielectric relaxation is observed in the frequency dependence of the dielectric constant. A discussion of the results in terms of domain switching processes is presented.

Variations of the dielectric constant of pzt ferroelectric ceramics with electric field

A distributed parameter delay line, with an electrically controlled delay time, was built and investigated. It uses the non-linear bias dependence of the dielectric constant of PZT ferroelectric ceramics. At room temperature, delay times of about 200 ns (at impedance level of 100 Ω) and variations of 10 percent with electric field were obtained.

https://ieeexplore.ieee.org/iel5/5/31170/01451129.pdf

Variable delay line based on the nonlinear characteristics of ferroelectric ceramics

A model, describing the electric field dependence of the dielectric constant of ferroelectric ceramics of tetragonal or rhombohedral symmetry, is presented. Perovskite type ferroelectric ceramics of tetragonal symmetry have two types of domains: 90° and 180° domains, while those with rhombohedral symmetry have three types: 71°, 109° and 180°. Since the dielectric behaviour of 71° and 109° domains in rhombohedral phase is actually similar to 90° domains in tetragonal phase, it is sufficient to take into account, for both symmetries, two types of domains: 90° and 180°. The ceramic is composed of a large number of domains of the two kinds. In the model, the coercive fields of these domains are described by two distribu- tion functions. The number of 180° and 90° switchings, caused by applying external d.c. field, is determined by the values of the distribution functions at various field values. This enables one to calculate the electric field dependence of the incremental dielectric constant. As a r...

A model of ferroelectric ceramics: Dielectric constant dependence on electric field

The electric field dependence of resonance frequency of a contour extensional mode of vibration in PZT ferroelectric ceramics was investigated. The bias characteristics of the resonance frequency showed a non-linear behaviour. A discussion of the results is given in terms of 90° domain rotations.The results indicate that rotation of 90° domains play an important role in the electric field dependence of physical constants in this material.

M. Brunstein

Papers

Electric field dependence of the dielectric constant of PZT ferroelectric ceramics

Variations of the dielectric constant of pzt ferroelectric ceramics with electric field

Variable delay line based on the nonlinear characteristics of ferroelectric ceramics

A model of ferroelectric ceramics: Dielectric constant dependence on electric field

Electric field dependence of a contour mode resonance in pzt ferroelectric ceramics