並列タイトル等マンガンおよび亜鉛の層状オキシハライドの高圧合成と結晶構造と物性
一般注記Over the past few decades, mixed anion compounds have drawn great attention because incorporation of two or more different anions with specific electronegativity, polarizability, ionic radius, and oxidation state offers opportunity to effectively cause chemical and physical properties that the pure oxides cannot possess. Among many mixed anion systems, A2B(O, X)4, a subgroup of the A2BO4-based oxide perovskites with the K2NiF4-type structure possesses different anion sites (i.e. equatorial and apical sites), leading to anion-site order in the anion sublattices. This situation is much different from that in the regular perovskite structure AB(O, X) which tends to disorder the anion sites. It is very important that accessibility to anion-siteordered states provides good advantage of understanding the role played by each anion in the structural, physical and chemical properties. Another aspect of anion lattice modification with hetero anions is that the electronic structures are changed in a way different from conventional cation substitution: anions are intimately bonded to cations, and thus anion substitution can effectively affect the coordination geometry or environment around the metal centers, which are closely correlated with the electronic structures of the compounds. In this thesis, we used a high pressure technique to synthesize new complex transition metal oxyhalides with the K2NiF4-type structure and studied their crystal structures and properties. Another member of layered oxyfluoride family, Sr2MnO3F was synthesized successfully with the high-pressure synthesis at 6 GPa and 1800 °C. It crystallizes into a simple body-centered tetragonal cell in the space group I4/mmm, with lattice parameters a = 3.79009(1) Å and c = 13.28974(6) Å. The manganese oxyfluoride exhibits unique structural features that have never been observed in any other related layered oxyhalides: the coexistence of anion disorder between O and F at the apical sites and the octahedral coordination subject to the 1st order Jahn-Teller effect. The MnO2 planes separated by non-magnetic Sr(O/F) rock-salt layers result in low-dimensional magnetic correlations with TN = 133 K, which is totally different from paramagnetic behaviors observed in known related layered manganese oxyfluorides. A new layered perovskite zinc oxychloride, Sr2ZnO2Cl2, with an infinite ZnO2 square planar sheet has been successfully synthesized by high pressure method. For Zn coordination environment, this square planar is quite unique and rare. Sr2ZnO2Cl2 isostructural with Sr2CuO2Cl2, a well-known parent material of high-Tc superconducting cuprates. The lattice constants of the zinc oxycloride are a = 4.06981(2) Å and c = 15.20076(8) Å at room teperature. The UV-vis-NIR absorption spectroscopy revealed an indirect band gap of Eg = 3.66 eV. The first principles calculation demonstrated that the origin of the indirect band gap was correlated with the square planar geometry for Zn: a transition between the top of the valence band comprising the anti-bonding state between Zn 3dx2-y2 and O 2p orbitals and the bottom of the conduction band derived from Zn 4s orbitals. A possible ideal two-dimensional square-lattice antiferromagnet Sr2MnO2Cl2 was successfully synthesized by high pressure method at 6 GPa and 1500 °C. It adopts a simple body-centered tetragonal cell in the space group I4/mmm. From the magnetic susceptibility measurement, the manganese ion was found to have a high spin state of S = 5/2. The susceptibility curve also showed a broad maximum at Tmax = 42K, which is typical behavior of the low dimensional antiferromagnets. No anomaly associated with a long-range magnetic order was observed down to 2 K, which was consistent with the result of the heat capacity measurement with a broad curve centered at 40 K. Neutron powder diffraction study demonstrated that a short-range magnetic correlation developed below 100 K but not to a long-range magnetic order down to 2 K. This is the first experimental observation of no long-range magnetic ordered state in square lattice antiferromagnets.
(主査) 教授 武田 定, 教授 忠永 清治, 客員教授 山浦 一成, 准教授 長浜 太郎, 客員准教授 辻本 吉廣
総合化学院（総合化学専攻）
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受理日（W3CDTF）2017-12-04T02:02:48+09:00
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