Metal-insulator transition inCa1−xLixPd

Abstract

Metal-insulator transition in Ca1−xLixPd3O4 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 preditcion [Phys. Rev. B62, 13426 (2000)], CaPd3O4 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.

Thermoelectric Properties of Layered Pd Oxide R2PdO4(R = La, Nd, Sm, and Gd)

“…The low sintering temperature of 1073 K prevented cations from evaporating from the pellets, which was verified through the composition analyses of Ca 1−x Li x Pd 3 O 4 previously. [8] We did not check the oxygen content, but as shown below, the magnitude of the thermopower of R 2 PdO 4 is 200-600 µV/K at 300 K, clearly indicating that they are almost undoped. This implies that the formal valence of Pd is close to 2+, and that the oxygen content is almost 4.…”

“…Polycrystalline samples of R 2 PdO 4 (R = La, Nd, Sm and Gd) and Nd 1.9 Ce 0.1 PdO 4 were prepared by a solidstate reaction using a NaCl-flux technique [8]. Stoichiometric amounts of…”

“…Recently, Ca 1−x Li x Pd 3 O 4 turned out to be a good p-type thermoelectric material [8], and Ca 1−x Bi x Pd 3 O 4 was found to be an n-type material [9]. Ca 1−x Bi x Pd 3 O 4 is the first example of the n-type Pd oxide, and is interesting in the sense that electrons are doped in the d x 2 −y 2 band separated from the d 3z 2 −r 2 band by a small energy gap of 0-10 meV.…”

The Role of Structural and Compositional Heterogeneities in the Insulator-to-Metal Transition in Hole-Doped APd3O4 (A = Ca, Sr)

“…Ichikawa and co-workers reported a transition in CaPd 3 O 4 around 10 mol % Li doping onto the Ca site. 16 However, when Na was used as a dopant, Itoh, Yano and Tsuda reported 30 mol % was necessary to drive the transition and remarked how processing can affect the observed electronic properties. 17,26 In the system Sr 1−x Na x Pd 3 O 4 , Taniguchi and co-workers reported a transition around 10 mol % Na.…”

“…13 Many complex palladium oxides have been previously shown to undergo compositional insulator-to-metal transitions. [14][15][16][17][18] The small bandgaps and significant Pd-d states just below the Fermi level in complex palladium oxides allows for the ease of hole-doping. Previous studies have suggested that some palladium oxides may have unique gapless electronic structures that can lead to interesting physics, 19,20 though these results may be influenced by the tendency of some DFT functionals to underestimate bandgaps in small bandgap semiconductors.…”