Interplay between Size, Composition, and Phase Transition of Nanocrystalline Cr³⁺-Doped BaTiO₃ as a Path to Multiferroism in Perovskite-Type Oxides

Abstract

Multiferroics, materials that exhibit coupling between spontaneous magnetic and electric dipole ordering, have significant potential for high-density memory storage and the design of complex multistate memory elements. In this work, we have demonstrated the solvent-controlled synthesis of Cr(3+)-doped BaTiO(3) nanocrystals and investigated the effects of size and doping concentration on their structure and phase transformation using X-ray diffraction and Raman spectroscopy. The magnetic properties of these nanocrystals were studied by magnetic susceptibility, magnetic circular dichroism (MCD), and X-ray magnetic circular dichroism (XMCD) measurements. We observed that a decrease in nanocrystal size and an increase in doping concentration favor the stabilization of the paraelectric cubic phase, although the ferroelectric tetragonal phase is partly retained even in ca. 7 nm nanocrystals having the doping concentration of ca. 5%. The chromium(III) doping was determined to be a dominant factor for destabilization of the tetragonal phase. A combination of magnetic and magneto-optical measurements revealed that nanocrystalline films prepared from as-synthesized paramagnetic Cr(3+)-doped BaTiO(3) nanocrystals exhibit robust ferromagnetic ordering (up to ca. 2 μ(B)/Cr(3+)), similarly to magnetically doped transparent conducting oxides. The observed ferromagnetism increases with decreasing constituent nanocrystal size because of an enhancement in the interfacial defect concentration with increasing surface-to-volume ratio. Element-specific XMCD spectra measured by scanning transmission X-ray microscopy (STXM) confirmed with high spatial resolution that magnetic ordering arises from Cr(3+) dopant exchange interactions. The results of this work suggest an approach to the design and preparation of multiferroic perovskite materials that retain the ferroelectric phase and exhibit long-range magnetic ordering by using doped colloidal nanocrystals with optimized composition and size as functional building blocks.

Molten salt route of single crystal barium titanate nanowires

“…It is well known that the 2u ranging between 44 and 46 is commonly used to distinguish the phase structure between cubic and tetragonal BaTiO 3 , where the single (200) peak characteristic of the cubic phase splits into the two tetragonal peaks of (200) and (002). [23,24] So, in order to further investigate the phase structure of BaTiO 3 nanowires, XRD measurements with slow scanning rate of 0.12 /min were done at 2u around 45 . For our sample, two diffraction peaks at 2u D 45.…”

A new LaCo0.71(1)V0.29(1)O2.97(3) perovskite containing vanadium in octahedral sites: synthesis and structural and magnetic characterization

“…A clear difference of IKβ′ for the BiLa 2 Co 2 SbO 9 and LaCoO 3 compounds can be seen, the IKβ′ for the first being higher than that for the second. This is not the case for LaCo 0.71(1) V 0.29(1) O 2.97 (3) and LaCoO 3 compounds, where the IKβ′ are very similar. Therefore the BiLa 2 Co 2 SbO 9 nominal spin is greater than LaCoO 3 and both LaCo 0.71(1) V 0.29(1) O 2.97 (3) and LaCoO 3 have spin states which can be considered to be similar.…”

“…The tilt is consistent with the space group Pnma (#62) and with the Goldschmidt tolerance factor which lies slightly below unity, τ = 0.96. τ was calculated using the well known formula: Combined refinements of PXRD and PND data were performed by allowing the variation of the occupancies of the metal ions in octahedral sites and O 2− sites, resulting in a small amount of oxygen vacancies. Thus, the refined crystallographic formula can be written as LaCo 0.71(1) V 0.29(1) O 2.97 (3) .…”

“…Moreover if the material can present oxygen vacancies, all these characteristics make this material very interesting from a technological point of view (catalysis, SOFC, ionic conductors, etc.). In the present article we describe the synthesis and structural and magnetic characterization of the new simple perovskite LaCo 0.71(1) V 0.29(1) O 2.97 (3) . We have used powder X-ray diffraction (PXRD) and powder neutron diffraction (PND), magnetization vs. temperature measurements, Co ion oxidation state determination from X-ray absorption spectroscopy (XAS), K β X-ray emission spectroscopy (XES) and thermogravimetric analysis (TGA).…”

Anisotropy in morphology and crystal structure of BaTiO3 nanoblocks

“…4 (a)). This displacement brings the creation of a polarization of 26 μC/cm 2 along the 〈001〉 direction [17,20,31,32], and induces residual strain in BaTiO 3 [33]. Xia, et.al mentioned that the internal strain in the lattice was related with the anisotropic growth of nanocrystals [34].…”