Ti-doping effect on the MI transition of hollandite vanadate,K2V8O16

Isobe, Masahiko; Koishi, Shigenori; Ueda, Yutaka

doi:10.1016/j.jmmm.2006.10.1087

Cited by 10 publications

(9 citation statements)

References 3 publications

(4 reference statements)

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“…Ti was found to form a complete solid solution system, K 2 V 8Ày Ti y O 16 , with a tetragonal I4=m structure. 21) With the substitution of Ti, the lattice parameter a first changes little and then increases linearly up to 10 21) Since no single crystal was obtained for the K 2 V 8Ày Ti y O 16 system, the transition was investigated by magnetic susceptibility and X-ray diffraction measurements. The MI transition characterized by the reduction in ðTÞ increases in temperature with the substitution of Ti but rapidly disappears at y > 0:5, as seen in Fig.…”

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confidence: 99%

Substitution Effect on Metal–Insulator Transition of K₂V₈O₁₆

et al. 2009

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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.

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Substitution Effect on Metal–Insulator Transition of K₂V₈O₁₆

et al. 2009

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“…In general, the substitution of different atoms introduces any disorder in the system and is expected to give a significant effect on the phase transition. Actually the substitution of Ti for V makes the transition broad and finally the transition smears out [4]. On the other hand, in K 2-x Rb x V 8 O 16 the transition does not show any broadening with increasing x.…”

Section: Resultsmentioning

confidence: 91%

“…From these results we proposed a possible charge order model, where two kinds of double-chain formed by V 3+ and V 4+ chains and by single V 4+ chains, respectively, order in a manner that gives a superlattice of √2 x √2 in the ab-plane, and the [3]. Recently we reported Ti-substitution effect on the MI transition [4]. A slight amount of Tisubstitution for V atoms raises the transition temperature and simultaneously the Ti-substitution makes the transition broad, leading to the final smearing out around y = 0.6 in K 2 V 8-y Ti y O 16 [4].…”

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confidence: 98%

“…Recently we reported Ti-substitution effect on the MI transition [4]. A slight amount of Tisubstitution for V atoms raises the transition temperature and simultaneously the Ti-substitution makes the transition broad, leading to the final smearing out around y = 0.6 in K 2 V 8-y Ti y O 16 [4]. In order to elucidate the origin of the transition, we have investigated the substitution effect of Rb for K sites.…”

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confidence: 99%

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Rb-substitution effect on the metal-insulator transition of hollandite vanadate, K₂V₈O₁₆

Isobe

Koishi

Ueda

2008

J. Phys.: Conf. Ser.

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Abstract. Rb-substitution effect on the metal-insulator transition of hollandite vanadate, K 2 V 8 O 16 has been investigated. The metal-insulator transition is accompanied by a charge ordering and a structural change from a tetragonal to a monoclinic structure with an increase of volume in the low-temperature monoclinic insulator phase. Rb-substitution for K atoms continuously raises the transition temperature up to 240 K for Rb 2 V 8 O 16 from 160 K for K 2 V 8 O 16 and does not make the transition broad in contrast to Ti-substitution. This significant rise of transition temperature can be understood as a negative chemical pressure effect caused by Rb-substitution.

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“…This configuration allows for the desired electrical properties in the catalyst because the cation freely gives its electrons to the surrounding ring resulting in mixed (+3/+ 4) valences on the Ru sites [29]. The details of the tunnel-like structure of hollandites can be found in several previous studies [29][30][31][32][33][34][35][36][37]. Conversely, if the hollandite itself is not active, then it is reasonable to conclude that the hollandite acts as precursor from which Ru and K are placed in close proximity following decomposition; this may be responsible for the enhanced performance of these catalysts.…”

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Characterization of K-Promoted Ru Catalysts for Ammonia Decomposition Discovered Using High-Throughput Experimentation

et al. 2008

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We obtain H 2 from low temperature NH 3 decomposition using a new hollandite (KRu 4 O 8 ) catalyst supported on c-Al 2 O 3 discovered using high-throughput experimentation and advanced TEM/SEM characterization. Relative to the base Ru°catalyst, this new catalyst shows NH 3 conversion enhancements of 30-50% at T = 350°C and decomposition activity at temperatures decreased by 50-100°C. TEM analysis over the lifetime of the catalyst shows multiple phases and morphologies suggesting that the KRu 4 O 8 behaves either as a new low-temperature decomposition catalyst or as a precursor to the active catalyst.

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Ti-doping effect on the MI transition of hollandite vanadate,K2V8O16

Cited by 10 publications

References 3 publications

Substitution Effect on Metal–Insulator Transition of K₂V₈O₁₆

Substitution Effect on Metal–Insulator Transition of K₂V₈O₁₆

Rb-substitution effect on the metal-insulator transition of hollandite vanadate, K₂V₈O₁₆

Characterization of K-Promoted Ru Catalysts for Ammonia Decomposition Discovered Using High-Throughput Experimentation

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Ti-doping effect on the MI transition of hollandite vanadate,K2V8O16

Cited by 10 publications

References 3 publications

Substitution Effect on Metal–Insulator Transition of K2V8O16

Substitution Effect on Metal–Insulator Transition of K2V8O16

Rb-substitution effect on the metal-insulator transition of hollandite vanadate, K2V8O16

Characterization of K-Promoted Ru Catalysts for Ammonia Decomposition Discovered Using High-Throughput Experimentation

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Substitution Effect on Metal–Insulator Transition of K₂V₈O₁₆

Substitution Effect on Metal–Insulator Transition of K₂V₈O₁₆

Rb-substitution effect on the metal-insulator transition of hollandite vanadate, K₂V₈O₁₆