Thermal Expansion, Thermoelectric Power, and XPS Studyof the Nonmetal-Metal Transition in Ni1-xS1-ySey

Matoba, Masanori; Anzai, S.; Fujimori, A.

doi:10.1143/jpsj.60.4230

Cited by 53 publications

(28 citation statements)

References 42 publications

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“…(19) of the thermoelectric power analysis of the Cu x Co y Cr z Se 4 spinel system From the results of the magnetic considerations presented in Table 1 it follows that with increasing cobalt content y: (1) contribution of superexchange interaction to the Curie-Weiss temperature θ CW suddenly increases from 90 K for y = 0.0 to 206 K and remains almost constant in the compositional range 0.06 ≤ y ≤ 0.11, (2) contribution of double-exchange interaction to the Curie-Weiss temperature θ CW and the total hopping integral B slowly decrease, (3) the W d bandwidth of the 3d t 2g band due to Cr 3+ and Cr 4+ ions decreases from 0.76 eV for y = 0.0 to 0.24 eV for y = 0.11, (4) the superexchange J aa and J ab integrals for the first two coordination spheres are positive and negative, respectively, and they change their signs on opposite in single crystal with y = 0.23. The absolute value of J aa is over seven times larger than J ab , (5) the double exchange b aa and b ab integrals for the first two coordination spheres are positive and their values are two times larger in comparison with the superexchange ones, (6) the effective exchange constants J aa eff and J ab eff for the first two coordination spheres are positive and negative, respectively, and they change their signs on opposite in single crystal with y = 0.23.…”

Section: Results Of Calculationsmentioning

confidence: 99%

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Effect of double exchange on thermoelectric power of CuxCoyCrzSe4

Groń

Mazur

Duda

et al. 2009

Journal of Alloys and Compounds

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Section: Results Of Calculationsmentioning

confidence: 99%

“…Conventional theory of metals [18][19][20] predicts that thermopower consists of a diffusion component, which according to the Mott formula [21] is proportional to temperature and a phonon drag component, which is more complex. The theory of the phonon drag thermopower is well established [21][22][23].…”

Section: Thermopower Theorymentioning

confidence: 99%

Effect of double exchange on thermoelectric power of CuxCoyCrzSe4

Groń

Mazur

Duda

et al. 2009

Journal of Alloys and Compounds

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Section: Abstract: D Optical Properties D Phase Transitionsmentioning

confidence: 99%

“…Effects of substituting other elements for Ni or S have been also studied in detail. 7,8 Recently, two high-resolution photoemission studies 9,10 have revealed a finite density of states (DOS) around the Fermi energy (E F ) in the LT phase, but they have given contrasting interpretations: Nakamura et al 9 have concluded that there is a small correlation-induced band gap with an unusually sharp band edge, and that the observed finite DOS at E F is due to thermal and instrumental broadenings of the edge. On the other hand, Sarma et al 10 have concluded that the LT phase is an "anomalous metal".…”

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confidence: 99%

Optical study of the metal–nonmetal transition in NiS

Okamura

Naitoh

Nanba

et al. 1999

Solid State Communications

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Optical reflectivity study has been made on the hexagonal (NiAs-type) Ni 1−δ S in order to probe its electronic properties, in particular those associated with the metal-nonmetal transition in this compound. Samples with δ=0.005 and 0.02 are studied, which have transition temperatures Tt=246 K and 161 K, respectively. A pronounced dip appears in the reflectivity spectra upon the transition, and the optical conductivity spectra show that the electronic structure below Tt is similar to that of a carrier-doped semiconductor with an energy gap of ∼ 0.15 eV. The optical spectra indicate that the gap becomes larger with decreasing temperature, and it becomes smaller as δ increases. It is also found that the overall spectrum including the violet region can be described based on a charge-transfer-type semiconductor, consistent with recent photoemission results. Keywords: D. optical properties, D. phase transitionsThe problem of the metal-nonmetal phase transition in the hexagonal NiS has been studied for three decades, but the transition mechanism is not completely understood yet. The high temperature (HT) phase above the transition temperature, T t ∼ 260 K, is a paramagnetic metal. Upon cooling through T t , the resistivity increases suddenly by a factor of ∼ 40, associated with slight increase in the lattice constants (0.3 % in a and 1 % in c) and the appearance of an antiferromagnetic order.1-3 T t is lowered sharply with increasing Ni vacancies, and the transition disappears when the vacancy content exceeds ∼ 4 %.4 Similar behavior is observed also with an applied pressure, and the transition is not observed at pressures above ∼ 2 GPa.5 These behaviors are summarized in the phase diagram of Fig. 1.The nature of the low-temperature (LT) phase below T t has been studied by many experiments. The resistivity (ρ) increases only slightly with cooling, with an activation energy of several meV.4 In contrast, an optical study by Barker and Remeika 6 clearly showed the presence of an energy gap of about 0.15 eV. Hall effect experiment by Ohtani 4 has shown that the majority carrier in the LT phase is the hole, and the density of holes is proportional to that of Ni vacancies, with ∼ 2 holes per Ni vacancy. Namely, the LT phase can be described as a p-type degenerate semiconductor, where the Ni vacancies act as acceptors. Effects of substituting other elements for Ni or S have been also studied in detail. 7,8 Recently, two high-resolution photoemission studies 9,10 have revealed a finite density of states (DOS) around the Fermi energy (E F ) in the LT phase, but they have given contrasting interpretations: Nakamura et al.9 have concluded that there is a small correlation-induced band gap with an unusually sharp band edge, and that the observed finite DOS at E F is due to thermal and instrumental broadenings of the edge. On the other hand, Sarma et al. 10 have concluded that the LT phase is an "anomalous metal".Various models have been proposed to account for the phase transition and the gap opening in NiS. At early stage, it wa...

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“…[1][2][3][4][5][6][7] The main origin of these properties is the d electrons of transition metal ions. Historically, the starting point of research on d electrons was a series of studies on Mott insulators including charge-transfer-type insulators.…”

Section: Introductionmentioning

confidence: 99%

Tetragonal Phase Change by Copper Solution in Nickel Oxide

Suzuki

Kamekawa

Nakayama

et al. 2010

Trans. Mat. Res. Soc. Japan

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Nickel copper oxide ((Ni 1-x Cu x )O) thin films, where the Cu content x was changed in the range from 0 to 1, were prepared by pulsed laser deposition. The copper content of the thin films was determined by energy-dispersive X-ray analysis with scanning electron microscopy. Transmission electron microscope observations of the thin film with x=0.52 revealed that the unit cell was distorted from cubic to tetragonal according to the Jahn-Teller effect by Cu 2+ ions dissolved in the NiO lattice. Key words: (Ni,Cu)O, Jahn-Teller effect, tetragonal, pulsed laser deposition, crystal structure INTRODUCTIONTransition metal oxides show various physical phenomena such as the metal-insulator transition, high temperature superconductivity, and enormous magnetic resistance. 1-7) The main origin of these properties is the d electrons of transition metal ions. Historically, the starting point of research on d electrons was a series of studies on Mott insulators including charge-transfer-type insulators. According to band theory, transition metal oxides should show metallic electrical conduction properties, but some of them are insulators because their d electrons are localized at each transition metal ion by a repulsive force between electrons. Among transition metal oxides, nickel oxide (NiO) is a charge-transfer-type insulator. 8) It has a NaCl-type (B1) structure and exhibits antiferromagnetism below the Néel temperature (T N = 523 K). These properties of NiO have been exploited in a variety of applications. It is known that NiO thin films are suitable for use in magnetoresistance sensors, electrochromic devices, transparent conducting films, and chemical sensors . [9][10][11] Various attempts have been made to add alloying elements into NiO. For example, it has been reported that in the Ni-Li-O system, hole carriers are introduced into NiO by substituting Li atoms for Ni since Li is ionized to Li + . 12) A Ni-Li-O phase has been used as a negative-temperature-coefficient thermistor. A Ni-Fe-O phase shows ferromagnetism caused by double-exchange interaction at room temperature, and is anticipated to be suitable for use in diluted magnetic semiconductor (DMS) applications. [13][14] The Ni-Nb-O system includes a phase being regarded as a promising catalyst used to substitute Nb 5+ for Ni 2+ . 15) In the Ni-Zn-O system, the addition of Zn into NiO has been observed to alter the electron structure and cause excitation from O(p) ->Ni(d) to O(p) -> Zn(s) as a result of Zn 2+ substitution. 16) Studies on NiO are expected to lead to new DMS and catalytic applications.In the present study, we attempted to add Cu 2+ ions into NiO. It is well known that Cu 2+ ions (d9) in an octahedral environment cause lattice distortion brought about by the Jahn-Teller effect. 17) The common

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Thermal Expansion, Thermoelectric Power, and XPS Studyof the Nonmetal-Metal Transition in Ni_1-xS_1-ySe_y

Cited by 53 publications

References 42 publications

Effect of double exchange on thermoelectric power of CuxCoyCrzSe4

Effect of double exchange on thermoelectric power of CuxCoyCrzSe4

Optical study of the metal–nonmetal transition in NiS

Tetragonal Phase Change by Copper Solution in Nickel Oxide

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