Antiferroelectricity and ferroelectricity in epitaxially strained PbZrO3from first principles

Abstract

Density functional calculations are performed to study the effect of epitaxial strain on PbZrO3. We find a remarkably small energy difference between the epitaxially strained polar R3c and nonpolar Pbam structures over the full range of experimentally accessible epitaxial strains -3 % η 4 %. While ferroelectricity is favored for all compressive strains, for tensile strains the small energy difference between the nonpolar ground state and the alternative polar phase yields a robust antiferroelectric ground state. The coexistence of ferroelectricity and antiferroelectricity observed in thin films is attributed to a combination of strain and depolarization field effects. [2,3] in that its structure is obtained through distortion of a nonpolar high-symmetry reference structure; for ferroelectrics the distortion is polar, while for antiferroelectrics it is nonpolar. However, not all nonpolar phases thus obtained are antiferroelectric; in addition, there must be an alternative ferroelectric phase obtained by a polar distortion of the same reference structure, close enough in free energy so that an applied electric field can induce a first-order phase transition from the antiferroelectric to the ferroelectric phase, producing a characteristic polarization-electric field (P-E) double-hysteresis loop. The electric-field-induced transition is the source of functional properties and promising technological applications. Non-linear strain and dielectric responses at the phase switching are useful for transducers and electrooptic applications [4,5]. The shape of the double hysteresis loop suggests applications in high-energy storage capacitors [6,7]. In addition, an effective electro-caloric effect can also be induced in systems with a large entropy change between the two phases [8].Lead zirconate PbZrO 3 (PZO) was the first material identified as antiferroelectric [9]. Despite extensive studies and characterization, PZO continues to offer insights into the origin and complexity of antiferroelectricity [10,11]. In bulk form, PZO has a cubic perovskite structure at high temperatures and a nonpolar orthorhombic ground state below T c ∼ 505 K. The ground state has space group Pbam [12, 13] and unit cell dimensions √ 2a 0 × 2 √ 2a 0 × 2a 0 with respect to the reference lattice constant a 0 . Its distorted perovskite structure is derived from the cubic (C) unit cell through a nonpolar Σ 2 distortion mode of Pb +2 ion displacements in the 110 C direction, combined with oxygen octahedron rotation R − 5 modes around the 110 C axis (a − a − c 0 in Glazer notation). Under an applied electric field, PZO single crystals undergo a first order phase transition into a sequence of polar phases with rhombohedral symmetry [14]. Similar rhombohedral polar phases are observed in the polycrystalline ceramic system Pb(Zr 1−x Ti x )O 3 under small 5-10 % isovalent substitution of zirconium for titanium [15,16]. In thin films, the competition between the rhombohedral low-energy structures and the PZO ground state is less studied. Room temperature ...

Critical Thickness for Antiferroelectricity inPbZrO3

“…The thickness dependent behavior of the polycrystalline films was tentatively attributed to the interface layer between the film and electrode. The possibility to stabilize the FE phase in PbZrO 3 by epitaxial compressive strain at zero Kelvin was later established in first principles simulations [11]. At the same time the epitaxial stain effects cannot explain one of the earliest experimental reports of a size-driven AFE-FE transition in PbZrO 3 films and BiNbO 4 films [7].…”

“…On the other hand, antiferroelectrics appear to demonstrate just the opposite behavior upon scaling down. More precisely, they were reported to develop a ferroelectric phase at the nanoscale [7][8][9][10][11]. It seems that the effects that arise at the nanoscale are capable of inducing a transition between the polar and antipolar phases of the same material.…”

Multiple Soft-Mode Vibrations of Lead Zirconate

“…In fact, the AF oxides are promising materials for high-energy storage capacitors, high-strain actuators and perhaps even for electrocaloric refrigerators [1][2][3]. The interest in the improvement of our understanding of AF oxides has been expressed recently [1,2,4,5].Lead zirconate, PbZrO 3 , is the best known example of an AF oxide -it is an end-member of technologically relevant solid solutions with PbTiO 3 (piezoelectric PZTs) [1,2,4,[6][7][8]. The parent paraelectric phase is a simple cubic perovskite with a 5-atom unit cell (P m3m, Z=1).…”

“…Before discussing the novel experimental results, let us note that the state-of-art density functional theory calculations have clearly demonstrated that the parent cubic structure of PbZrO 3 is unstable at low temperatures with respect to the Pb ion off-centering as well as concerted oxygen octahedra tilts [5,12,[17][18][19][20]. These calculations show a system of unstable branches, dominated by Pb-O vibration, and including Γ 15 , M 5 , M 2 , X 5 , X 2 and R 15 phonon modes, as well as a few unstable branches connecting the rigid-body oxygen-octahedra tilt modes M 3 , X 5 and R 25 (throughout the paper, we are using the labels of Ref.…”

First-principles study of the multimode antiferroelectric transition inPbZrO3

“…Full relaxation (via other structural modes not considered here) lead to a further energy decrease of only 3 meV/fu, which confirms the dominant character of Q Σ , Q R and Q S . Competing phases.-Earlier studies suggest that the equilibrium P bam phase of PZO competes with other FE, AFE, and AFD structures [17,21,[23][24][25]. We thus ran a series of computer experiments to shed some light on why PZO chooses such an unusual phase over more common alternatives.…”