A Mossbauer and X-ray diffraction investigation of Li-Ti ferrites

Abstract

Li0.5+0.5xTixFe2.5-1.5xO4, x<or=0.7, has been investigated using X-ray powder diffraction (17-70 degrees 2 theta ) and Mossbauer spectroscopy (300 and 77 K). All compositions show single cubic spinel structure with a constant lattice parameter of 0.833 nm. The room temperature Mossbauer spectra gave magnetic sextets which broadened with increasing x; in addition, a small paramagnetic component started to develop for higher Ti substitution. The 77 K measurements are less broadened, but the intensity of the central doublet has not changed. The Zeeman patterns were fitted with two models: two six-line Lorentzian subspectra assigned to the tetrahedral and octahedral sites and a distribution of magnetic hyperfine fields. The hyperfine fields at both temperatures for the A and B sites decrease as x increases, but at a faster rate for the former site when x>0.3. Similar distribution profiles have been deduced using the latter model. An asymmetric distribution is observed for x<or=0.4, with the hyperfine fields derived from the Lorentzian fit falling inside the distribution. As x increases a peak at lower hyperfine fields develops and becomes more prominent as x increases. The influence of Li and Ti substitution on the hyperfine field is discussed.

The influence of TiO2 polymorph, mechanical milling and subsequent sintering on the formation of Ti-substituted spinel-related Li0.5Fe2.5O4

“…[1,5,6]. Normally, the material is prepared by the conventional ceramic double sintering method in which solid state reactions between oxides and/or carbonates of Li, Fe(III) and Ti(IV) require prolonged heat exposure at elevated temperatures (typically ∼1200ºC) [1,7,8]. One of the disadvantages of high temperature sintering is the volatility of Li 2 O and the irreversible reduction of Fe 3+ to Fe 2+ with the consequent precipitation of α-Fe 2 O 3 and…”

Crystal and Magnetic Structure of the System Li0.5+0.5xFe2.5−1.5xTixO4 (x=0.16, 0.44, and 0.72)

“…Previous studies by X-ray diffraction were first reported by Blasse [1] and described these phases as cation-ordered for x % 0.33 and disordered for 0.55 x 1.11, with again an ordered distribution for higher degrees of substitution, 1.11 x 1.66. This range of composition was confirmed by Schaner, [2] although Yousif [4] proposed that this system shows the 1:3 ordering for x < 0.7. In addition, other authors [1][2][3][4][5] have reported detailed studies using magnetization and Mössbauer spectroscopy for this system in the range 0 x 0.7, in agreement with the cation distribution proposed by Blasse [1] and White.…”

“…These transitions are accompanied by noticeable variations in the magnetic behaviour and a many studies on this system have been reported in the literature, [1][2][3][4][5][6][7][8] owing to their high transition temperature from ferromagnetic to paramagnetic, as occurs in the parent phase, Li 0.5 Fe 2.5 O 4 , for which the transition temperature is as high as 958 K. [9][10][11] Though much research has been carried out about the physical properties of these derivatives and the main features of their structure and relations are now well known, there are still some controversies, especially over the composition range at which structural changes occur, and over the magnetic structure and the effect of nonmagnetic and magnetic cation substitution on various properties of lithium ferrites. [1,[12][13] The first member of this solid solution, Li 0.5 Fe 2.5 O 4 (that is, with x = 0) is an inverse spinel that can be formulated as (Fe 3 + ) A [Li 0.5 Fe 1.5 ] B O 4 . It crystallizes in the space group P4 3 32 and has a cation ordering of 1:3-type in the octahedral sublattice [9] (being located Li + in 4b and Fe 3 + in 12d sites), and the different charge of cations seem to be the responsible for this ordering.…”

Cation Distribution Study of Chromium Substituted Copper Nickel Zinc Ferrite

“…The cation distribution for each concentration and the site preferences of cations distributed among the tetrahedral (A) and octahedral [B] The mean ionic radius of the tetrahedral A-and octahedral B-sites (r A and r B ) was calculated [12,13]. It is observed that radius of tetrahedral site 'r A ' remains constant at (0.712 Ǻ) whereas radius of octahedral site 'r B ' decreases with increasing Cr 3+ substitution (Table 2 and Figure 6).…”