(Ni,Cu)O Phase in Thin Films Prepared by Pulsed Laser Deposition

Kamekawa, Takayuki; Asami, Hiroki; Suzuki, Tsuneo; Nakayama, Tadachika; Suematsu, Hisayuki; Yunogami, Takashi; Niihara, Koichi

doi:10.1143/jjap.47.584

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“…Preparation of thin films in a nonequilibrium state can be realized by physical vapor deposition techniques, and we have succeeded in the synthesis of various metastable materials by pulsed laser deposition (PLD). [21][22][23] In previous research 24) , it was clarified that both interplanar distances and lattice constants increased with increasing copper content, and the (Ni 1-x Cu x )O phase with 0<x<0.27 has a B1 structure. The purpose of the present investigation was to prepare supersaturated (Ni,Cu)O thin films with x>0.27 by PLD, to determine the crystal structure of the (Ni,Cu)O thin films, and to discuss a crystal distortion factor by Cu 2+ solution into NiO.…”

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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Section: Introductionmentioning

confidence: 99%