EFFECT OF EPITAXIAL STRAIN ON THE STRUCTURAL AND FERROELECTRIC PROPERTIES OF Bi₂FeCrO₆ THIN FILMS

Abstract

Bi 2 FeCrO 6 thin films were epitaxially grown by pulsed laser deposition on (100)-oriented LaAlO 3 , (LaAlO 3 ) 0.3 (Sr 2 LaTaO 6 ) 0.7 and SrTiO 3 single crystalline substrates with and without epitaxial CaRuO 3 buffered layer. The in-plane compressive strain induces monoclinic distortion of the Bi 2 FeCrO 6 lattice cell. The strain originates from lattice mismatch between CaRuO 3 and single crystal substrates. The similar crystal structure of the substrate and the layer lead to coherent epitaxial growth of the heterostructures and avoid strain relaxation in particular for BFCO films deposited on LaAlO 3 substrates. The ferroelectric character is demonstrated for all grown BFCO films. The residual in-plane strain weakly affects the effective piezoelectric coefficient of BFCO layers.Keywords: Pulsed laser deposition (PLD); perovskite thin films; complex oxides; epitaxy; piezoresponse (PFM); crystal structure; cation ordering; double perovskite.An important area of research in recent years has been to understand exactly why the properties of epitaxial films differ from related bulk materials, and to learn how to use these differences to engineer desirable properties. Effects due to strain in the films are often thought of as analogous to those of high pressure experiments in bulk. The main differences are (i) the stress in the films is typically biaxial rather than hydrostatic or uniaxial, (ii) films can have much larger strains than is usually achievable in pressure cells, and (iii) films are easier to work with for many experiments and applications. Ferroelectricity in strained perovskite films has been a particularly noteworthy topic of study. Recent experiments have shown strain-induced ferroelectricity in SrTiO 3 (STO) films, and huge changes in the ferroelectric transition temperature T C in both STO and BaTiO 3 (BTO) films under strain. 1,2 Other notable results include large changes in the metal-insulator transition temperature of NdNiO 3 films under strain 3 and reports of increasing the transition temperature of La 2−x SrCuO 4 under compressive strain. [4][5][6] In this letter, we present a systematic investigation of structural and ferroelectric properties in epitaxial Bi 2 FeCrO 6 (BFCO) films with varying degree of compressive strain by using several commercially available single crystal substrates. * Corresponding author.X-ray diffraction (XRD) patterns collected on polycrystalline BFCO film (400 nm) deposited on amorphous SiO 2 (100 nm) on Silicon (100) by laser ablation were fitted with a rhombohedral R3 unit cell similar to that previously reported for BiFeO 3 (BFO). 7 The rhombohedral lattice parameter of this BFCO film is found to be around 5.56 Å which corresponds to a pseudo-cubic lattice parameter of ∼ 3.93 Å. Recently, Suchomel et al. reported the synthesis of high pressure BFCO bulk. 8 They claimed that BFCO bulk has a hexagonal R3c unit cell and the refined lattice parameters, obtained from the high resolution synchrotron XRD data are a = 5.5454 Å and c = 13.6952 Å. These values of latti...

Epitaxial Bi2FeCrO6 Multiferroic Thin Film as a New Visible Light Absorbing Photocathode Material

“…A careful analysis of the normalized intensity of the superstructure peaks was carried out to quantify the degree of Fe/Cr cationic ordering (R), which was estimated from the normalized ratio of the superlattice peak intensity to the main (111) reflection intensity of BFCO in the pseudocubic indexing ( Table 1 ). These results contrast those from our earlier study . The discrepancy is attributed to the different growth temperature used in the present study, a crucial parameter that determines the cationic ordering …”

“…This reveals highly compressive‐strained epitaxial layers throughout the whole heterostructure that originate from the lattice mismatch between the film and the substrate (Table S1, Supporting Information). The strain of CRO buffered layer leads to fully coherent epitaxial growth of the heterostructure and precludes strain relaxation, especially for the BFCO film deposited on LAO substrate, in agreement with previous work …”

“…[ 28,29 ] A careful analysis of the normalized intensity of the superstructure peaks was carried out to quantify the degree of Fe/Cr cationic ordering (R), which was estimated from the normalized ratio of the superlattice peak intensity to the main (111) refl ection intensity of BFCO in the pseudocubic indexing [ 30 ] ( Table 1 ) those from our earlier study. [ 25 ] The discrepancy is attributed to the different growth temperature used in the present study, a crucial parameter that determines the cationic ordering. [ 24 ] X-ray photoelectron spectroscopy (XPS) was used to identify the chemical composition and oxidation states present in different BFCO thin fi lms ( Figure S6, Supporting Information).…”

“…The strain of CRO buffered layer leads to fully coherent epitaxial growth of the heterostructure and precludes strain relaxation, especially for the BFCO fi lm deposited on LAO substrate, in agreement with previous work. [ 25 ] Since the B site-cationic ordering in double perovskite materials of the type A 2 BB ′ O 6 (displayed in Figure S4, Supporting Information) plays a crucial role in determining the magnetic properties and tuning the optical characteristics, evidence of its existence is an important step toward understanding and controlling the functionalities of such materials. [ 23,26,27 ] As observed from the different types of stacking in BFCO crystals (Figure 2 a,b), the alternation of FeO 6 and CrO 6 planes is achieved only in the (111) cubic direction.…”

Origin of lowered magnetic moments in epitaxially strained thin films of multiferroicBi2FeCrO6

“…Thus, for our calculations we constructed a 20-atom √ 2 × √ 2 × 2 tetragonal supercell (inset in Fig.1a), starting from a simple cubic double perovskite structure, to allow for appropriate magnetic ordering of ions along (111) direction. Using the experimental in-plane pseudo-cubic lattice parameter a cub = 3.93Å [13,18] as reference we generated structures mimicking the epitaxially-strained films by varying the in-plane lattice parameter. The in-plane lattice parameters for our supercell were set toā =b = √ 2 × a cub while the c parameter was relaxed for each in-plane strain.…”