M.A. Spears

Conduction in titanate pyrochlores: role of dopants

Electrical conductivity measurements have been performed on the pyrochlore compounds Y2Ti2O7, Gd2Ti2O7 and Sm2Ti2O7 as a function of temperature, oxygen fugacity and aliovalent dopant concentration. Both the magnitude and type of conduction (ionic and/or electronic) were found to be influenced by dopant size, site location (“A” or “B” cation sublattice) and net dopant density. While Ca doping on the “A” cation sublattice (CaGd,Sm,Y) was found to increase the ionic conductivity by as much as two and half orders of magnitude, Sr and Mg dopants with larger dopant-host size mismatch induced a drop in ionic and an enhancement in electronic conductivity. Acceptor doping on the “B” cation sublattice, e.g. AlTi, increased the ionic conduction only at low dopant levels, while RuTi enhanced electronic conduction at high PO2. Trends in ionic and electronic conduction as a function of T, PO2, and dopant density are analyzed with the aid of a defect chemical model.

Modelling and characterization of mixed ionic-electronic conduction in Gd2(Ti1 − xMnx)2O7 + y

Abstract Mixed ionic and electronic conductivity was obtained in Gd 2 Ti 2 O 7 by doping with Mn. This was confirmed by measuring the nonstoichiometry and the electrical conductivity as a function of oxygen partial pressure, temperature and Mn concentration. The results were combined with the defect and transport models, to derive key thermodynamic and kinetic parameters of Gd 2 Ti 2 O 7 doped with Mn.

Mixed Ionic-Electronic Conduction in Pyrochlore Oxides

The transport properties of the pyrochlore solid solution Gd 2 (Zr x Ti l-x ) 2 O 7 are investigated to clarify the relationships between composition, structural disorder and ionic and electronic transport. The oxygen ion conductivity has been found to increase sharply with increasing Zr content, x, due to enhanced structural disorder, leading to intrinsic ionic conduction at large values ofx. In contrast, the n—type conductivity predominant at low x, decreases sharply above x=0.2. Defect chemical models are presented to account for the simultaneous contributions of both intrinsic and dopant induced disorder. These models are applied to the σ(T, PO 2 , dopant) data to extract key thermodynamic and transport parameters. The significance of these parameters and the potential application of these materials in electrochemical devices are discussed.

Electrical properties and defect structure of polycrystalline doped barium titanium niobate

The authors present the preliminary results of a study of the defect chemistry of barium titanium niobate (BTN) and Ba/sub 6-1.5x/La/sub x/Ti/sub 2/Nb/sub 8/O/sub 30/ (BLTN). A preliminary model for the defect chemistry of BLTN is presented, and the trends in conductivity with composition, temperature, and p/sub 02/ are shown, for sintered compacts of BLTN with lanthanum content from 0% to 20%. The major lattice defects in these compositions are tentatively identified, and an estimate of the thermal bandgap is derived.<<ETX>>