Crystal Structure Analysis of Epitaxial BiFeO₃–BiCoO₃ Solid Solution Films Grown by Metalorganic Chemical Vapor Deposition

Abstract

Epitaxial (001)-oriented (1 À x)BiFeO 3 -xBiCoO 3 solid solution films with x ¼ 0 { 0:33 were grown on (100)SrTiO 3 substrates at 700 C by metalorganic chemical vapor deposition. The crystal structure of the films was characterized by high-resolution X-ray diffraction analysis and Raman spectroscopy. Unit cell volume and the lattice parameter were changed with increasing x. The BiFeO 3 film with x ¼ 0 has rhombohedral symmetry and those with x ¼ 0:16 and 0.21 have a mixture of rhombohedral and tetragonal symmetries. Finally, tetragonal symmetry was observed for the film with x ¼ 0:33 together with a small amount of the contamination phase. This result suggests that the symmetry of (1 À x)BiFeO 3 -xBiCoO 3 films changed from rhombohedral to tetragonal with increasing x similarly to Pb(Zr,Ti)O 3 having a large piezo response.

Composition control and thickness dependence of {100}-oriented epitaxial BiCoO3–BiFeO3 films grown by metalorganic chemical vapor deposition

“…8,9 In our previous study, we reported the crystal symmetry change with film composition x in xBiCoO 3 -͑1−x͒BiFeO 3 for 200 and 400 nm thick films and found that the crystal symmetry differed between these film thicknesses around x = 0.16 composition. 5,6 Hence, a crystal symmetry change occurs at a film thickness near this composition.…”

“…[5][6][7] This system has a phase boundary between tetragonal and rhombohedral symmetries through an intermediate monoclinic symmetry, similar to a PbTiO 3 -based system with a large piezoelectricity, such as PbTiO 3 -PbZrO 3 , PbTiO 3 -Pb͑Zn 1/3 Nb 2/3 ͒O 3 , and PbTiO 3 -Pb͑Mg 1/3 Nb 2/3 ͒O 3 . 8,9 In our previous study, we reported the crystal symmetry change with film composition x in xBiCoO 3 -͑1−x͒BiFeO 3 for 200 and 400 nm thick films and found that the crystal symmetry differed between these film thicknesses around x = 0.16 composition.…”

Emerging Multiferroic Memories

“…Bulk work on BiCoO 3 [205] and theoretical predictions of giant electronic polarization of more than 150 μC/cm 2 [206] have driven researchers to attempt creating this phase as a thin film as well. To date only solid solutions of BiFeO 0 -BiCoO 3 have been grown via MOCVD [207]. Another phase similar to BiCoO 3 that has been produced as a thin film is PbVO 3 [22], PbVO 3 films were grown on LaAlO 3 , SrTiO 3 , (La 0.18 Sr 0.82 )(Al 0.59 Ta 0.41 )O 3 , NdGaO 3 , and LaAlO 3 /Si substrates and were found to be a highly tetragonal perovskite phase with a c/a lattice parameter ratio of 1.32.…”

Ferroelectric Properties of Bi1.1Fe1-xCoxO3 Thin Films Prepared by Chemical Solution Deposition Using Iterative Rapid Thermal Annealing in N2 and O2

“…33 similarly to Pb(Zr,Ti)O 3 with a large piezoresponse. 19) Naganuma et al prepared the 5 wt % Co-BiFeO 3 thin films at 500 C by conventional chemical solution deposition (CSD) using onetime RTA in air, which is dominated by nitrogen and oxygen. 20) As bismuth is a highly volatile element, BFO thin film deposition requires the use of Bi-excess precursors to compensate for the Bi loss at nominally employed high growth temperatures.…”