Effects of the synthesis procedure, doping and non-stoichiometry on the order–disorder transformation in LnTiO (Ln=Tm–Lu) oxygen-ion conductors

Study of bulk and grain-boundary conductivity of Ln2+xHf2−xO7−δ (Ln = Sm-Gd; x = 0, 0.096) pyrochlores

“…The high-conductivity DP phase of the Ln 2 Ti 2 O 7−δ titanates contains Ln 0 Ti þ Ti Ln antistructure pairs and oxygen vacancies in the temperature range of our conductivity measurements (450-950ºС). These defects may relax during cooling or storage if the samples were synthesized using co-precipitation [17]. Similar results were reported by Eberman et al [16] for (Sc z Yb 1−z ) 2 Ti 2 O 7 .…”

“…Similar results were reported by Eberman et al [16] for (Sc z Yb 1−z ) 2 Ti 2 O 7 . However, in the synthesis of titanates with the use of mechanical activation followed by firing, Ln 0 Ti þ Ti Ln cation defects may be stabilized, as was found for Yb 2 Ti 2 O 7 , which was shown to contain about 4.5% Yb 0 Ti þ Ti Yb anti-structure pairs at room temperature [17]. In the Ln 2+x M 2−x O 7−δ (Ln = Sm−Gd; M = Zr, Hf; x=0−0.286) systems, anti-structure pairs (5-22%) were found at room temperature in Ln 2 M 2 O 7 (M = Zr, Hf) samples synthesized using mechanical activation [9].…”

“…In quent high-temperature heat treatment influences the defect structure of the titanates. At the same time, the fact that defects (4.5%) were found in Yb 2 Ti 2 O 7 at room temperature after high-temperature synthesis from a mechanically activated mixture [17] suggests that mechanical activation may produce defects in appropriate symmetrical structures and that some of the defects may persist after high-temperature annealing. Since the M 4+ −O bonds in the hafnates and zirconates are less covalent than those in the titanates [19], mechanical activation of Ln 2 M 2 O 7 (Ln = Sm − Gd; M = Zr, Hf) is also quite likely to produce anti-site defects.…”

Structural Characterization and Photoluminescent Properties of (La1–xSmx)2Ti2O7 Solid Solutions Synthesized by a Sol–Gel Route

“…[6] Moreover, these compounds have a high Curie temperature, which is particularly interesting for high-temperature piezoelectric applications. [7,8] However, Ln 3+ ions with small radii (Ln = Sm-Lu) generally adopt a pyrochlore structure [9,10] with no known ferroelectric properties. The stability of the structure depends on the ratio between the radii (r) of the Ln 3+ and Ti 4+ cation sites.…”

Fabrication of Dy2Ti2O7 nanocrystalline at 700°C and its photocatalytic activity

“…Pyrochlore oxides have recently been the subject of extensive studies as potentially attractive dielectric materials, catalysts, solid electrolytes and radiation absorbers [1][2][3][4][5][6][7][8]. The pyrochlores have the general formula A 2 B 2 O 7 where A is the larger cation and B is the smaller one.…”