Ferroelectricity in Low-Permittivity SrZrO₃ Epitaxial Films

Abstract

Bulk SrZrO3 has an orthorhombic perovskite structure (Pbnm) with a central symmetry but exhibits a low dielectric constant. In this study, we reported a room-temperature ferroelectric SrZrO3 thin film with a low dielectric constant, induced by compressive strain from the SrTiO3 substrate. The presence of an out-of-phase boundary structure allows SrZrO3 with a large lattice mismatch to grow epitaxially on SrTiO3 substrates. The apparent atomic displacements in the lattice are revealed by scanning transmission electron microscopy imaging. Compressive strain induces an orthorhombic-to-monoclinic phase transition, evidenced by both the atomic structure obtained from the annular bright-field image and the structure optimized with first-principles calculation. Further first-principles calculations demonstrated that compressive strain causes a polar displacement of the Zr atom inside the ZrO6 octahedron, which is the origin of the ferroelectricity. Our work shows a way to design novel ferroelectrics from conventional non-ferroelectric materials, which is of significant importance to robust, stable, and lead-free ferroelectrics applications.

Stereointerface Structure Drives Ferroelectricity in BaZrO3 Films

“…The origin of the OPB structure is then investigated. In the study of SrZrO 3 thin film, it has been observed that the appearance of the OPB structure is related to strain relaxation, suggesting that the OPB structure may be derived from lattice mismatch . A 7.5% lattice mismatch exists between bulk BZO and substrate STO, and the RSM results show that strain relaxation occurs in BZO thin films.…”

“…There are multiple mechanisms for the formation of OPB structure, with the use of steps or terraces on the substrate surface being one of the most common induction strategies. , Another approach for constructing OPB structures is to generate different phases or atom stack faults in thin films via nonstoichiometry. ,, The mismatch distortion caused by the large lattice mismatch between the film and substrate can also serve as the nucleation site for the OPB structure . Recently, we have observed the OPB structure in SrZrO 3 thin films . The emergence of the OPB structures is accompanied by the occurrence of strain relaxation, and as atoms are stacked, the OPB structure extends to the surface of the film, suggesting that the nucleation and expansion of the OPB structure have a significant relationship with the clamping effect of the substrate.…”

Insights into Strain Engineering: From Ferroelectrics to Related Functional Materials and Beyond

“…This scenario is also consistent with experimental observations . In addition, compressive epitaxial strains have been demonstrated to suppress antiferrodistortive-mode-associated ORRs and favor room-temperature ferroelectricity in CaTiO 3 -type paraelectrics, including tetragonal CaTiO 3 films (ε = −1.7% for LaSrAlO 4 substrates) and monoclinic SrZrO 3 films (ε = −5% for SrTiO 3 substrates) …”

“…Antiferromagnetic paramagnetic or nonmagnetic ground states are naturally predominant in most materials, and intricate interactions (e.g., the “ d 0 – d n ” dilemma of 3 d oxides) further hinder the integration of ferroelectricity and ferromagnetism into one system . To fully release the potential of these materials, strain engineering has been utilized to explore more unprecedented multiferroics, including EuTiO 3 , − A MnO 3 (where A is an alkaline-earth metallic atom Ca, Sr, or Ba), − SmMnO 3 , , and even paraelectric/nonmagnetic SrTiO 3 mediated by chemical, pressure, or local lattice strains. , The centrosymmetric cubic G-type antiferromagnetic structure of EuTiO 3 (a cubic lattice possessing a P m-3m space group and a T N of 5.5 K) impedes the emergence of coexisting magnetoelectrics, while in the TiO 6 coordination environment, the Ti 3 d 0 configuration and unpaired Eu 4 f 7 electrons ( S = 7/2), provide an avenue to simultaneously achieve ferroelectric and ferromagnetic ordering analogous to that in the type I BeFeO 3 multiferroic. Theoretical calculations have manifested that the 3-fold degeneracy of the TO 1 phonon mode is disrupted by a – b planar biaxial strains .…”

Screening Aluminum-Based Compounds as Low-κ Dielectrics for High-Frequency Applications

“…Several materials have been proposed as alternatives to silica, including AlPO 4 –BPO 4 –SiO 2 ternaries, cordierite, − and several borates. − The characteristics of these compounds suggest that compounds with low atomic number atoms and open frameworks should be prioritized. Furthermore, the search for low-κ materials should be contrasted with efforts to find inorganic high-dielectric constant materials and ferroic materials − where traditionally second-order Jahn–Teller ions such as Ti 4+ and lone-pair ions such as Bi 3+ are used . These works actually aid in the search for low-κ materials by suggesting which ions should be best avoided.…”