Antiferroelectrics: History, Fundamentals, Crystal Chemistry, Crystal Structures, Size Effects, and Applications
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Received: 26 January 2021 | Revised: 19 March 2021 | Accepted: 22 March 2021 DOI: 10.1111/jace.17834 INVITED FEATURE ARTICLE Antiferroelectrics: History, fundamentals, crystal chemistry, crystal structures, size effects, and applications Clive A. Randall1 | Zhongming Fan1 | Ian Reaney2 | Long- Qing Chen1 | Susan Trolier- McKinstry1 1Materials Research Institute and Material Science and Engineering, The Abstract Pennsylvania State University, University Antiferroelectric (AFE) materials are of great interest owing to their scientific rich- Park, PA, USA ness and their utility in high- energy density capacitors. Here, the history of AFEs is 2University of Sheffield, Sheffield, UK reviewed, and the characteristics of antiferroelectricity and the phase transition of an Correspondence AFE material are described. AFEs are energetically close to ferroelectric (FE) phases, Clive A. Randall, Materials Research and thus both the electric field strength and applied stress (pressure) influence the Institute and Material Science and Engineering, The Pennsylvania State nature of the transition. With the comparable energetics between the AFE and FE University, University Park, PA, USA. phases, there can be a competition and frustration of these phases, and either incom- Email: [email protected] mensurate and/or a glassy (relaxor) structures may be observed. The phase transition Funding information in AFEs can also be influenced by the crystal/grain size, particularly at nanometric National Science Foundation, Grant/ dimensions, and may be tuned through the formation of solid solutions. There have Award Number: IIP- 1841453 and been extensive studies on the perovskite family of AFE materials, but many other 1841466 crystal structures host AFE behavior, such as CuBiP2Se6. AFE applications include DC- link capacitors for power electronics, defibrillator capacitors, pulse power de- vices, and electromechanical actuators. The paper concludes with a perspective on the future needs and opportunities with respect to discovery, science, and applications of AFE. KEYWORDS applications, dielectric materials/properties, ferroelectricity/ferroelectric materials, phase transition 1 | INTRODUCTION OF THE AFE process that involves the ordering of pre-existing dipoles that were disordered in the high- temperature PE phase. Antiferroelectric (AFE) materials have identifiable sponta- The phase transition between PE- AFE occurs at a critical neously ordered dipole moments that are arranged antipar- temperature, Tc. On the application of an electric field of allel so as to cancel out on a unit-cell basis at zero field, but sufficient strength, the material can switch from the low- for which an electric field of sufficient magnitude can induce temperature AFE phase to a FE phase with a polar space a phase transition to a ferroelectric (FE) phase with parallel group (Figure 1A).4,5 dipole ordering, as illustrated in Figure 1A. The AFE phase In a phenomenological description, a phase transition is is typically a consequence of a structural phase transition typically described by an order parameter or a set of order from a higher temperature phase known as the prototype parameters.6 In the case of the AFE, there are two sublat- and/or paraelectric (PE) phase.1– 23 It takes place through ei- tices with the same magnitude of spontaneous polarization ther a displacive soft-mode transition or an order–disorder but in opposite directions, leaving a net-zero macroscopic J Am Ceram Soc. 2021;104:3775–3810. wileyonlinelibrary.com/journal/jace © 2021 The American Ceramic Society | 3775 3776 | RANDALL ET AL. FIGURE 1 (A) Schematic representation of paraelectric, antiferroelectric, and ferroelectric states in PbZrO3 (oxygen octahedral tilting not shown). (B) Typical double hysteresis loop measured in Pb0.98La0.02(Zr0.66Ti0.10Sn0.24)0.995O3 (replot from Ref. [7]) [Color figure can be viewed at wileyonlinelibrary.com] FIGURE 2 Key pioneers in the first 20 years of antiferroelectric discovery and development (1951– 1970) polarization within the crystal structure at zero field. 2 | EARLY AFE PIONEERS AND Figure 1B shows a typical double hysteresis curve mea- KEY DISCOVERIES FROM THE 7 sured in Pb0.98La0.02(Zr0.66Ti0.10Sn0.24)0.995O3. Associated FIRST 20 YEARS with AFE- FE switching, there is a critical forward coer- cive field, EF, that is the field- induced AFE- to- FE phase 2020 was the 100- year anniversary of the discovery of fer- transition. Then, on reducing the forward field, there is a roelectricity by Valasek (1920) in Rochelle salt. In that switch back to the AFE phase at a different coercive field, work, the polarization–electric field (P-E) hysteresis invited EA. On reversing the field direction, similar transitions are analogies to ferromagnetic materials, and hence the use of 8 observed at -E F. After saturation of the FE polarization at the word “ferro” as a prefix to the dielectric analog. Anti- high fields, on reducing electric field strength to - EA, the ferromagnetism has been known as a phenomenon since the FE reverts to the AFE phase. As will be discussed below, work of Louis Néel, in the 1930s.9 Following the discovery observation of double hysteresis alone does not provide of ferroelectricity in the perovskite BaTiO3— in various lo- conclusive proof of a phase being AFE, as double hyster- cations, including United States, Russia, and Japan (and esis can also arise from randomly oriented defect dipoles possibly Germany), during WWII, as scientists looked for in an aged FE and/or switching of a FE with a first- order alternative dielectric materials to replace mica for capaci- 10– 14 phase transition temperature above the Curie tempera- tor applications— antiferroelectricity was discovered. ture (Tc). Below, the experimental characteristics of AFE Figure 2 shows photos of some of the critical pioneers in phases are described which collectively aid in identifying AFE materials from 1951 to 1970. a material as AFE. Before considering these characteris- The first reports on AFEs were from the Tokyo Institute tics, the history of the first 20 years of AFE materials is of Technology (Tokyo Tech), on the perovskite AFE discussed. PbZrO3, in two publications from Shirane, Sawaguchi, RANDALL ET AL. | 3777 Takeda, (1950) and Sawagachi, Maniwa, and Hoshino beyond the first 20 years. Nonetheless, those first 20 years (1951).15– 17 Kittel, at Bell Labs in 1951, provided the first underpinned many of the important characteristics that guide theoretical justification, suggesting that antiferroelectricity current understanding. should exist.18 Shirane came to Penn State and joined the X- ray structural group of Pepinsky, who at that time had a very advanced structural refinement laboratory and used 3 | EMPIRICAL PROPERTY diffuse scattering to aid structural determinations of polar CHARACTERISTICS ASSOCIATED symmetries and calculate the electron density maps around WITH AN AFE PHASE atoms. He used structural analytics to discover FE and re- lated materials across many different crystal structures. By There are several empirical observations that aid the determi- 1953, the second AFE phase was published and refined; nation and verification of an AFE phase. Below, a number of 19 this was the perovskite, PbHfO3. At that time, Newnham these properties, ranging from the double hysteresis, crystal- was a student at Penn State working in the Pepinsky group, lographic structure, unit cell volume, stress dependence of and he published with Shirane and Pepinsky (1954) the the transition temperature, field dependence of the permit- 20,21 crystal structure of the AFE NaNbO3. tivity, low thermal conductivity, and negative electrocaloric Meanwhile, in the United Kingdom at the University coefficient, are considered. of Leeds, Cross and Nicholson were also working on 22 NaNbO3 crystals and were able to show double hysteresis. Simultaneous to the experimental work, and inspired by the 3.1 | Polarization– electric field switching recent power of the Devonshire phenomenological modeling in the form of double hysteresis loops of the BaTiO3 FE materials, Cross utilized the postulates in the Kittel publication and introduced a model to account for Antiferroelectricity is characterized by the ability to induce 23 the double hysteresis observations in NaNbO3. a phase transition between a non- polar AFE phase and a Outside of the perovskites, Keeling and Pepinsky (1955) polar FE phase, producing remarkable changes in properties. studied the low- temperature (148 K) behavior of Ammonia To observe the switching, the dielectric material must have Di- Hydrogen Phosphate (NH4)H2PO4 (ADP) and determined the appropriate crystallographic structure with antiparallel the order– disorder H- displacement with AFE sublattice sym- spontaneous polarizations; the coercive fields for the trans- metry breaking.24 formation must be sufficiently low as to minimize conductiv- Another important step came with Cochran (following ity and/or dielectric breakdown. So, in order to permit the work of Raman, Frohlich, Ginzburg, Landau, Anderson, field forcing the switching and thereby observe the dielectric and Landauer and colleagues) with the elucidation of the double hysteresis response, it is imperative to minimize the soft mode theory for displacive phase transitions (1959).25 extrinsic dielectric loss associated with conductivity of ionic Although it was initially introduced for ferroelastics, it was or electronic space charge contributions that can screen and generally applicable to many displacive phase transitions,