High-Pressure Phase Transformation of Cobalt Monoxide Due to Electronic Transition

Noguchi, Yuichi; Atou, Toshiyuki; Kondo, Tadashi; Yagi, T.; Syono, Yasuhiko

doi:10.1143/jjap.38.l7

Cited by 17 publications

(12 citation statements)

References 63 publications

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“…Eto et al compressed NiO up to 141 GPa ͑Ref. 15͒ and no changes were observed, in contrast to other monoxides: CoO ͑80 Gpa͒, 16 FeO ͑90 GPa͒, 17 and MnO ͑present case͒. This fact supports our model.…”

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confidence: 86%

Pressure-induced metallization of MnO

et al. 2005

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Optical absorption and IR reflection measurements of MnO were performed under various pressures up to 140 GPa at room temperature. In IR reflection measurement, a drastic increase in reflectivity due to the metallization is observed from 94 GPa. On the other hand, in absorption, it is observed that the band gap does not close monotonously with pressure but accelerated extremely from 80 GPa, as indicated by an abrupt increase of an additional absorption tail located at the lower energy than the absorption edge. The absorption tail extends to 0 eV around 90 GPa, which is consistent with the IR reflection measurement. The pressure coefficient of the band gap shift is obtained to be −0.016 eV/ GPa up to 80 GPa.The manganese perovskite materials ͑RMnO 3 , where R is a rare earth metal͒ are exceptionally important Mott ͑or charge transfer͒ insulators since many interesting phenomena are observed including the colossal magnetoresistance ͑CMR͒, 1,2 half-metallic behavior, 3 and phase separation. 4 The main stage in such phenomena occurs in a MnO 6 octahedron and the actor is the d electrons in the manganese e g level split off from the t 2g level by the crystal field generated by six oxygen ions. When chemical pressure is applied by replacing the R-site ions, the transfer integral of manganese d͑e g ͒ electrons changes through the change of the Mn-O-Mn bond angle. MnO is the simplest manganese oxide and shows antiferromagnetic character at the temperature lower than T N = 118 K. The crystal has the NaCl-type ͑B1-type͒ structure above T N , and below the temperature, a slight contraction along a ͗111͘ direction occurs. It means that a manganese ion is surrounded by six oxygen ions and forms a MnO 6 octahedron. There are two methods for the metallization of the insulator: bandwidth control and band-filling control. In contrast with the filling control due to the doping or introduction of the defects, the bandwidth control by pressuring is able to conserve the system pureness. Furthermore, in MnO, the Mn-O-Mn bond angle is never changed by compression. Therefore, to study the physical properties of MnO under various pressures is regarded as that of the core of the manganese perovskites as the function of the Mn-O bond length. Recently, Kondo et al. 5 performed an x-ray analysis of MnO at room temperature and observed new phase boundaries at 30, 90, and 120 GPa. At that time, they also observed, by an optical microscope, that the sample becomes highly reflective above 90 GPa. There is a possibility that a metallic or semimetallic transition occurs near this pressure. For clarifying that a phase is true metallic, it is the best and the simplest way to show ͑i͒ high infrared ͑IR͒ reflectivity or ͑ii͒ both low specific resistance and its decreasing nature with decreasing temperature, and in high pressure study, their pressure insensitivity. Although the transition has been investigated theoretically, 6,7 we present here, experimental evidence of transition to the true metallic phase.We performed the IR reflection and absorptio...

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confidence: 86%

Pressure-induced metallization of MnO

et al. 2005

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“…Here, the M atom is octahedrally coordinated by nitrogen atoms while the carbodiimide group experiences a trigonal-prismatic coordination by the metal atoms. Interestingly enough, this [NiAs] type of crystal structure is also found for both FeO and CoO, but only at high pressures. , …”

Section: Introductionmentioning

confidence: 63%

Electronic and Magnetic Structure of Transition-Metal Carbodiimides by Means of GGA+U Theory

et al. 2010

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The electronic structures and magnetic properties of MNCN (M = Fe, Co, and Ni) have been investigated by density-functional theory including explicit electronic correlation through an ad hoc Coulomb potential (GGA+U). The results evidence CoNCN and NiNCN as type-II anti-ferromagnetic semiconductors (that is, intralayer ferromagnetic and interlayer anti-ferromagnetic), in accordance with experimental observations. Just like the prototype MnNCN, the MNCN phases, with M = Ni and Co, thus resemble the corresponding MO monoxides with respect to their magnetic and transport properties. By contrast, FeNCN remains (semi)metallic even upon applying a strong Coulomb correlation potential. This, most probably, is in contradiction with its observed optical transparency and expected insulating behavior and points toward a serious density-functional theory problem.

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“…The displacive phase transition has also been observed in FeO (5), MnO (24), and CoO (23) under high pressures. MnO and CoO displayed multiple phase transitions under high pressures (23,24). Nevertheless, the distorted B1 phases transform to the B1 structure upon laser heating, and the B1 structure transforms back to the distorted phases after temperature quench (Fig.…”

Section: Experimental Methodsmentioning

confidence: 98%

Stability of magnesiowüstite in Earth's lower mantle

Lin

Heinz

Mao

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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[(Mg,Fe)SiO 3 ] (1, 2), which together are likely the most important mineral assemblage of Earth's interior. The stability of the magnesiowüstite and silicate perovskite plays a crucial role in understanding the geophysical and geochemical properties of Earth. At ambient conditions, the end members of the MgOFeO (periclase-wüstite) system form a solid solution and have the same rock-salt (B1) structure. Periclase remains in the B1 structure to at least 227 GPa (3, 4). Wüstite transforms to a rhombohedral structure at pressures above 18 GPa at 300 K (5) and then to the NiAs or anti-NiAs structure (6-8). The topological difference between the pressure-temperature (P-T) phase diagrams of periclase and wüstite indicates that regions of two-phase equilibria should exist. A thermodynamically calculated P-T-composition phase diagram for the system suggests that an increase in pressure in the system would result in a gradual exsolution of an almost pure FeO and an Fe-depleted (Mg,Fe)O (9). Recent studies of three magnesiowüstites [(Mg 0.5 ,Fe 0.5 )O, (Mg 0.6 ,Fe 0.4 )O, and (Mg 0.8 ,Fe 0.2 )O] in an externally heated diamond anvil cell (DAC) up to 86 GPa and 1,000 K suggested that magnesiowüstite decomposes into Mg-rich and Fe-rich magnesiowüstites (10, 11). The decomposition of magnesiowüstite was proposed to occur at the P-T conditions of the lower mantle (10, 11) and to contribute significantly to the seismic-wave heterogeneity of the lower mantle (12, 13). On the other hand, no evidence for a phase transformation in (Mg 0.6 ,Fe 0.4 )O was found in shock-wave experiments to 201 GPa (14). Here we report the in situ study of structure and stability of magnesiowüstites at P-T conditions of the lower mantle. A rhenium or stainless steel gasket was preindented to a thickness of 30 m and then a hole of 220-m diameter was drilled in it. An amorphous boron and epoxy mixture (4:1 by weight) was filled and compressed in the hole. Subsequently, another hole of 100 m was drilled and used as the sample chamber. A sandwich configuration, consisting of dried NaCl as the thermal insulator and pressure medium on both sides of the sample, was used (16-18). The amorphous boron provided higher strength to create a deeper sample chamber, giving stronger x-ray diffraction from a thicker sample and better laser-heating spots attributable to thicker thermal insulating layers. ʈ Moreover, use of amorphous boron as an inner gasket also avoided unwanted x-ray diffraction peaks from Re or the stainless steel gasket. Experimental MethodsWe have used a double-sided Nd:YLF (neodymium: yttrium lithium fluoride) laser heating system, operating in multimode (TEM 00 ϩTEM 01 ), to heat the sample from both sides of a DAC at the 13-IDD GeoSoilEnviro-Consortium for Advanced Radiation Sources (GSECARS) sector of the Advanced Photon Source, Argonne National Laboratory (18). The laser beam diameter was Ϸ25 m. Graybody temperatures were determined by fitting the thermal radiation spectrum between 670 nm and 830 nm to the Planck radiation function. The tempe...

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High-Pressure Phase Transformation of Cobalt Monoxide Due to Electronic Transition

Cited by 17 publications

References 63 publications

Pressure-induced metallization of MnO

Pressure-induced metallization of MnO

Electronic and Magnetic Structure of Transition-Metal Carbodiimides by Means of GGA+U Theory

Stability of magnesiowüstite in Earth's lower mantle

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