Synthesis and Thermodynamic Properties of the Ln2CrTaO7 (Ln = Sm, Gd, Y) Pyrochlores

Abstract

Ln 2 CrTaO 7 (Ln = Sm, Gd, Y) pyrochlores are synthesized by the co-precipitation with subsequent annealing. The effect of the precursor composition ((NH 4 ) 2 Cr 2 O 7 , Cr(NO 3 ) 3 , and CrCl 3 ) on the precipitates reactivity and product microstructure was studied. Samples with an average particle size of 200 nm for Y 2 CrTaO 7 , 450 nm for Gd 2 CrTaO 7 and 600 nm for Sm 2 CrTaO 7 were used to study thermodynamic properties. The temperature dependences of heat capacity were measured by the adiabatic calorimetry (13-346.16 K) method and the ratio method using DSC measurements (330-1300 K). The thermodynamic functions of Ln 2 CrTaO 7 compounds were calculated. The absence of polymorphic transitions up to a temperature of 1450°C for all studied compounds is shown.

XPS and NEXAFS Characterization of Mg/Zn and Mn Codoped Bismuth Tantalate Pyrochlores

“…Specifically, Ta4f and Ta5p spectra exhibit an energy shift of ∆E = 0.7 eV, while the Ta4d spectra exhibit an energy shift of 1 eV. This suggests that tantalum atoms have the same effective charge +(5-δ) as observed in similar spectra of tantalum in bismuth tantalates doped with Cr, Fe, Co, Ni, Cu atoms [21,22,24]. The shift of the Ta4f and Ta5p spectra for Bi 2 Mg 0.5 Mn 0.5 Ta 2 O 9.5−∆ and Bi 2 MgTa 2 O 9 may also be associated with the presence of a certain fraction of heterovalent manganese and magnesium ions in the tantalum(V) position.…”

“…Such doping options lead to the formation of a pyrochlore structure deficient in A cations, as is observed for bismuth-containing pyrochlores and is the reason for the relaxation properties of oxide ceramics [12,17]. Currently, almost all pyrochlores based on bismuth tantalate containing 3 ions (Cr,Fe,Co,Ni,Cu,Zn) are known and studied [18][19][20][21][22][23][24][25][26][27]. Due to their excellent dielectric properties, such pyrochlores are promising as multilayer ceramic capacitors, resistors, resonators, sensors and microwave filters.…”