Formation of LuFe₂O₄ phase from an undercooled LuFeO₃ melt in reduced oxygen partial pressure

Abstract

The formation of metastable phases from an undercooled LuFeO 3 melt was investigated under reduced Po 2 since the iron ion has the tendency to change its valence state from Fe 3+ to Fe 2+ in an ambient atmosphere with low Po 2 . The nucleation and the post-recalescence temperatures of the phases were decreased with decreasing process Po 2 . Phase equilibrium was established in the Lu-Fe-O system at 1473 K by varying the oxygen partial pressure from 10 5 to 10 −1 Pa. A possible ternary metastable phase diagram depending on the oxygen composition in the bulk sample was also constructed. The formation of the LuFe 2 O 4 phase where the Fe 3+ and Fe 2+ ratio is 1:1 clearly indicated that the formation of metastable phases is related to the presence of Fe 2+ ions. Thermogravimetric analysis revealed that the increase in sample mass with decreasing process Po 2 , down to 10 −1 Pa, is relatively dependent on the amount of Fe 2+ ions.

Growth diagram and magnetic properties of hexagonal LuFe2O4thin films

“…If three-dimensional (3D) island growth occurs, the RHEED images correspond to the diffraction pattern of the transmitted electron beam which contains more structural information. Figure 3 shows the RHEED images of the MgO (111) substrates and the LuFe 2 O 4 films with the electron beams directed along MgO [1][2][3][4][5][6][7][8][9][10] or MgO . The strong LuFe 2 O 4 (003), (006), and (009) peaks observed in Fig.…”

“…In this work, we start from the ternary phase diagram of the bulk Lu-Fe-O system, a section of which is shown in Fig. 1(a) at 1200 • C. 8,9 This system belongs to the D-type of lanthanoid-Fe-O compounds for which there are four stable three-element phases: LuFe 2 O 4 (A) and Lu 2 Fe 3 O 7 (B), LuFeO 3 (perovskite or P), and Lu 3 Fe 5 O 12 (garnet or G). 10 In principle, one way to form a single LuFe 2 O 4 phase is to keep atomic ratio Lu:Fe=1:2 and vary the O 2 pressure, as shown as a thick dashed line in Fig.…”

Composition‐Dependent Ferroelectricity of LuFeO3 Orthoferrite Thin Films

“…In agreement with ref. [33], the thermodynamic phase diagram (Figure S5, Supporting Information) constructed based on the calculated enthalpies of Fe 2 O 3 , Lu 2 O 3 , and LFO oxides indicates that the orthorhombic LFO structure is not stable, consistent with the depiction as a point in the ternary phase diagram, and can be stabilized by epitaxial growth.…”

“…LFO thin films with Lu/Fe ratios of 0.6, 0.8, 1.0, 1.2, and 1.5 were grown on (001)-oriented STO (insulating) and Nb-doped STO (NSTO, conductive) substrates with a = 3.905 Å (Figure 1a). There were no secondary phases observed in the wide angle range X-ray diffraction (XRD) scans (15°-80 o , Figure S1, Supporting Information) for any of the films, despite the fact that according to the Lu-Fe-O ternary phase diagram, [33] LFO does not accommodate significant excess Lu or Fe, instead forms additional phases such as LuFe 2 O 4 , Lu 3 Fe 5 O 12 , Lu 2 Fe 3 O 7 , hexagonal LuFeO 3 , or binary oxides when Lu/Fe differs from 1.0. Due to the ionic radius difference between Lu 3+ (86 pm) and Fe 3+ (60 pm), as the film becomes Lu-rich, the XRD peak position 2θ of (002) p (p denotes the pseudocubic notation) moves to a lower angle and the out-of-plane lattice parameter c p increases from 3.789 Å (Lu/Fe = 0.6), 3.793 Å (Lu/Fe = 0.8), 3.800 Å (Lu/Fe = 1.0), 3.820 Å (Lu/Fe = 1.2), to 3.846 Å (Lu/Fe = 1.5).…”

Present status of the experimental aspect ofRFe2O4study

“…The reported magnetic transition temperature seems to be a little lower than the stoichiometric sample, which indicates the presence of small amounts of ionic vacancies. Kumar et al reported the presence of a LuFe 2 O 4 phase during the synthesizing of LuFeO 3 with a gas floating crystal growth method [127].…”