Substitution Effect on Metal–Insulator Transition of K₂V₈O₁₆

Abstract

The effect of the substitution of various ions on the metal-insulator (MI) transition at 170 K in K 2 V 8 O 16 has been investigated. Both Rb and Ti form complete solid solution systems: K 2Àx Rb x V 8 O 16 and K 2 V 8Ày Ti y O 16 , respectively. The substitution of Rb for K or of Ti for V splits the transition into two transitions: the high-temperature transition is a first-order MI transition from a tetragonal structure to a tetragonal structure, and the low-temperature transition is a second-order transition to a monoclinic structure. In K 2Àx Rb x V 8 O 16 , the former terminates to an MI transition at around 220 K in Rb 2 V 8 O 16 , while the latter disappears at x > 0:6. In K 2 V 8Ày Ti y O 16 , both transitions disappear at y > 0:5. The substitution of Cr for V also results in a similar splitting of the transition and the rapid disappearance of both transitions. The substitution of Na or Ba for K suppresses the MI transition without any splitting of the transition, although the solubility of both ions is limited. These substitution effects reveal that the MI transition of K 2 V 8 O 16 consists of two parts: a first-order MI transition and a parasitic second-order structural transition; the substitution of some ions causes a clear splitting of these transitions, probably due to the difference between the chemical pressure effects on the two transitions. The first-order MI transition is very sensitive to charge randomness, suggesting the charge ordering nature of the MI transition, while the second-order structural transition is very sensitive to both charge and structural randomnesses.

Substitution effect on metal–insulator transition in Cu(Ir1−xMx)2S4 (M=Sn, Hf)

“…It may arise from the existence of extrinsic localized moments at non stoichiometry sites or another kind of lattice imperfection. The similar behavior at low temperature has been observed in many compounds, see examples [14,15]. The numerical value extracted from the susceptibility at lower temperatures using Curie-Weiss law is estimated to be approximately 0.10 B (formula unit) −1 .…”

Crystal Structure and Magnetic Properties of the Novel Hollandite Ba1.3Co1.3Ti6.7O16

“…The distortion from tetragonal to monoclinic typically occurs when the channels in the host framework are too large for the guest atoms. For Ba 1.3 Co 1.3 Ti 6.7 O 16 we observe the monoclinic struc- (1) ture variant. Although for examples of both tetragonal and monoclinic variants incommensurately modulated structure refinements were presented [e. g., 24 -27], from our single-crystal X-ray diffraction data we have no indications for a modulation.…”

“…Hollandites are characterized by frameworks of egde-and vertex-sharing octahedra forming one-dimensional tunnel structures which host larger cations. The general formula can be written according to A x M 8 O 16 with typically x ≥ 1, A = alkali metal, alkaline-earth metal or Pb 2+ , and M being a wide variety of cations with positive charges of 1, 2, 3, 4, or rarely 5. Although hollandites have been extensively studied due to potential applications, for example as solid-state electrolytes, electrode materials and catalysts, little attention has been paid to their magnetic properties [3 -5].…”

“…The quasi-one-dimensional structure of hollandites demonstrates a broad spectrum of complex quantummechanical phenomena at low temperatures, including one-dimensional electron conductivity in KRu 4 [6,7], a quantum phase transition in BaRu 6 O 12 [8], a metal-insulator transition in K 2 V 6 O 16 [9 -12] and Bi x V 8 O 16 [13,14], the appearance of ferromagnetism in the diluted semiconductor K x Ti 8 O 16 [15], phase transitions in K 2 Cr 8 O 16 from a paramagnet to a metallic ferromagc 2011 Verlag der Zeitschrift für Naturforschung, Tübingen · http://znaturforsch.com net and then to an insulating ferromagnet as the temperature is lowered [16].…”

Anomalous electronic states of hollandite-type transition-metal oxides

“…Then, we in particular study the quasi-one-dimensional electron conduction observed in K [2,3] is discussed in this respect. We also study the electronic structure of K 2 V 8 O 16 to consider the origins of the observed anomalous electronic states and metal-insulator transition [4]. (d 5.3 ).…”