The electrical resistivity ρ and the magnetic susceptibility χ were measured for the sintered samples of Ca 1- x La x RuO 3 (0≦ x ≦1) (La x ) and Ca 1- x Pr x RuO 3 ( x ≦0.2). The temperature coefficient dρ/d T is positive at 300 K for all the samples, but ρ increases logarithmically with decreasing temperature as for the Kondo effect except for the end members x =0 and 1. The Curie-Weiss like χ was found for La x , and the absolute value of the antiferromagnetic Weiss temperature increases with x until 0.3 and then decreases. For La 0.3 the Curie-type χ appeared overlapping the Curie-Weiss χ below 50 K, and there was no clear peak in χ down to 5 K. The resistance anomaly may have been caused either by the Kondo scattering, or a localization effect and/or an electron-electron interaction under the random distribution of hetero-valent cations.

Electrical and Magnetic Properties of Ca1-xLaxRuO3.

Metal-insulator transition in ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Li}}_{x}{\mathrm{Pd}}_{3}{\mathrm{O}}_{4}$ has been studied through charge transport measurements. The resistivity, the Seebeck coefficient, and the Hall coefficient are consistently explained in terms of a simple one-band picture, where a hole with a moderately enhanced mass is itinerant three dimensionally. Contrary to the theoretical prediction [Phys. Rev. B 62, 13 426 (2000)], ${\mathrm{CaPd}}_{3}{\mathrm{O}}_{4}$ is unlikely to be an excitonic insulator, and holds a finite carrier concentration down to 4.2 K. Thus the metal-insulator transition in this system is basically driven by localization effects.

Metal-insulator transition in Ca 1-x Li x Pd 3 O 4

The electronic energy band structure for cubic palladium oxides ${\mathrm{CaPd}}_{3}{\mathrm{O}}_{4}$ in the ${\mathrm{NaPt}}_{3}{\mathrm{O}}_{4}$ structure has been calculated by the full-potential linearized augmented-plane-wave method within the local-density approximation. ${\mathrm{CaPd}}_{3}{\mathrm{O}}_{4}$ is almost semiconducting, but has a very small number of carriers. We propose that this compound is a good candidate for being an excitonic insulator, similar to ${\mathrm{CaB}}_{6}.$ Moreover, the bands near the Fermi level have one-dimensional character.

CaPd 3 O 4 as an excitonic insulator

Insulator–metal transition induced in Sr1−xNaxPd3O4 for small Na-substitutions

Synthesis and characterization of electron and hole doped ternary palladium oxide : Sr1-xAxPd3O4 (A = Na, Bi)

The resistivity and the Seebeck coefficient were measured for sintered Ca 1- x Na x Pd 3 O 4 (0≦ x ≦1). There occurs a metal to insulator transition at x =0.3, and the material is nonmetallic for s...

Metal to insulator transition for Ca1-xNaxPd3O4

The magnetic susceptibility χ m was measured for Ca 1- x Na x Pd 3 O 4 between 2 K and 300 K. The intrinsic part of the observed χ m is expressed by both the Curie-Weiss and the Hasegawa-Moriya formula, and Ca 1- x Na x Pd 3 O 4 ( x >0.3) is a metal in which the magnetic interaction between itinerant electrons will be antiferromagnetic. When analyzed by the latter theory, the Coulomb repulsion energy at an atomic site becomes 4.9 eV to 3.3 eV depending on the carrier density. Similarity and dissimilarity with high- T c cuprates are discussed since the oxide is not superconducting at least above 2 K.

Yuji Yano

Papers

Metal to insulator transition for Ca1-xNaxPd3O4

Magnetic Susceptibility of Ca1-xNaxPd3O4