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論文

分散型光学系を用いた時間分解X線吸収分光法によるRh金属微粒子触媒のCO酸化反応における自発振動現象の詳細観測

松村大樹; 木村優作*; 辻卓也; 水木純一郎*

SPring-8/SACLA利用研究成果集(インターネット), 11(5), p.296 - 299, 2023/11

https://doi.org/10.18957/rr.11.5.296

自発振動現象を起こすRh金属微粒子触媒上のCO酸化反応について、分散型光学系による時間分解X線吸収分光法を用いた研究を実施した。定常ガスを一定温度で導入して、触媒反応の振動現象が起こっている最中のRh金属微粒子の構造変化について、1Hz程度のフレームレートで詳細観測した。触媒反応生成物であるCO $_{2}$ 濃度の時間変化とX線吸収分光法によるRh金属微粒子構造の時間変化とを比べると、両者は強く相関していることが見て取れた。振動構造の様式には、Rhの平均価数変化は階段状のものである一方CO $_{2}$ の生成量はパルス状の変化であるという違いがあり、これは金属Rh表面で短時間のみ吸着COが無い状態が実現されるという考えで解釈できた。

論文

Local Ir dedimerization followed by ligand-hole hopping in X-ray irradiated thiospinel

平賀晴弘*; 松村大樹; 堀金和正*; 水木純一郎*

Journal of Physics and Chemistry of Solids, 150, p.109870_1 - 109870_8, 2021/03

https://doi.org/10.1016/j.jpcs.2020.109870

被引用回数：0 パーセンタイル：0(Chemistry, Multidisciplinary)

The extended X-ray-absorption fine structure of a spinel CuIr $_{2}$ (S $_{0.95}$ Se $_{0.05}$ ) $_{4}$ powder sample, which has the charge-ordered temperature $T_{rm{CO}}$ = 190 K, was determined at the Ir $L_{3}$ edge for a wide temperature range. All the local structure parameters on the Ir-Ir bonds signified the second structural change at $T^{*} sim$ 70 K. Remarkably, the number of Ir dimers decreased by 10% below $T^{*}$ , which indicates partial dedimerization by X-ray irradiation. We also reanalyzed the resistance data of CuIr $_{2}$ S $_{4}$ with the variable-range hopping model by focusing on the density of states. The X-ray-induced decrease in resistance was quantitatively explained as a result of the increase in the density of states, which was attributed to the release of holes from the 10%-dedimerized Ir ions. We suppose that the released holes hop over the ligand chalcogen site.

論文

Electrochemical adsorption on Pt nanoparticles in alkaline solution observed using in situ high energy resolution X-ray absorption spectroscopy

草野翔吾*; 松村大樹; 石井賢司*; 田中裕久*; 水木純一郎*

Nanomaterials (Internet), 9(4), p.642_1 - 642_14, 2019/04

https://doi.org/10.3390/nano9040642

被引用回数：7 パーセンタイル：37.59(Chemistry, Multidisciplinary)

The oxygen reduction reaction (ORR) on Pt/C in alkaline solution was studied by in situ high energy resolution X-ray absorption spectroscopy. To discuss the X-ray absorption near-edge structure (XANES), this paper introduced the rate of change of the (RCD), which is an analysis method that is sensitive to surface adsorption. The surface adsorptions as hydrogen (below 0.34 V), superoxide anion (from 0.34 V to 0.74 V), hydroxyl species (from 0.44 V to 0.74 V), atomic oxygen (above 0.74 V), and -PtO $_{2}$ (above 0.94 V) were distinguished. It is clarified that the catalytic activity in an alkaline solution is enhanced by the stability of atomic oxygen and the low stability of superoxide anion/peroxide adsorption on the platinum surface.

論文

Local structure study of the iron-based systems of BaFeAs and LiFeAs by X-ray PDF and XAFS analyses

Li, S.*; 豊田真幸*; 小林義明*; 伊藤正行*; 池内和彦*; 米田安宏; 大谷彬*; 松村大樹; 浅野駿*; 水木純一郎*; et al.

Physica C, 555, p.45 - 53, 2018/12

https://doi.org/10.1016/j.physc.2018.10.003

被引用回数：1 パーセンタイル：5.02(Physics, Applied)

鉄系超伝導体のBaFeAsとLiFeAsの局所構造解析をX線PDF解析とXAFSを利用して行った。BaFeAsの構造相転移温度ではPDFで得られた局所構造には変化が見られたが、EXAFSで得られた局所構造には変化を見出すことができなかった。これらのデータは室温の平均構造が正方晶相において、局所的な斜方歪みを考慮する必要があることを示唆している。

論文

Effect of -site randomness on the antiferroelectric/relaxor nature of the ground state; Diffuse and inelastic X-ray scattering study of Pb(In $_{1/2}$ Nb $_{1/2}$ )O

大和田謙二*; 塚田慎也*; 福田竜生; 筒井智嗣*; Baron, A. Q. R.*; 水木純一郎*; 大和英弘*; 安田直彦*; 寺内暉*

Physical Review B, 98(5), p.054106_1 - 054106_10, 2018/08

https://doi.org/10.1103/PhysRevB.98.054106

被引用回数：3 パーセンタイル：15.56(Materials Science, Multidisciplinary)

The effect of -site randomness on the antiferroelectric/relaxor nature of the ground state was investigated by studying diffuse and inelastic X-ray scattering from ordered and disordered Pb(In $_{1/2}$ Nb $_{1/2}$ )O (O- and D-PIN) single crystals. The diffuse scattering measurement of O-PIN (antiferroelectric at ) shows the existence of ferroelectrically interactive local polarization above . Inelastic X-ray scattering shows that the transverse-acoustic (TA) and transverse-optic (TO) modes are dominant at 800 K, while the central peak (CP) and TA modes are coupled and majorly contribute to the critical behavior of the diffuse scattering at . Upon these results, the -site randomness is discussed in terms of suppressing the antiferroelectric instability and enhancing the polarization fluctuation.

論文

Observation of momentum-dependent charge excitations in hole-doped cuprates using resonant inelastic X-ray scattering at the oxygen edge

石井賢司*; 遠山貴巳*; 浅野駿*; 佐藤研太朗*; 藤田全基*; 脇本秀一; 筒井健二*; 曽田繁利*; 宮脇淳*; 丹羽秀治*; et al.

Physical Review B, 96(11), p.115148_1 - 115148_8, 2017/09

AA2017-0402.pdf:0.81MB

https://doi.org/10.1103/PhysRevB.96.115148

被引用回数：29 パーセンタイル：77.9(Materials Science, Multidisciplinary)

We investigate electronic excitations in La $_{2-x}$ (Br,Sr)CuO using resonant inelastic X-ray scattering (RIXS) at the oxygen edge. We observed momentum-dependent spectral weight below 1 eV, which is consistent with theoretical calculation of the dynamical charge structure factor on oxygen orbitals in a three-band Hubbard model. Our results confirm that the momentum-dependent charge excitations exist on the order of the transfer energy (), and the broad spectral line shape indicates damped and incoherent character of the charge excitations at the energy range in the doped Mott insulators.

論文

Study of catalytic reaction at electrode-electrolyte interfaces by a CV-XAFS method

草野翔吾*; 松村大樹; 朝澤浩一郎*; 岸浩史*; 坂本友和*; 山口進*; 田中裕久*; 水木純一郎*

Journal of Electronic Materials, 46(6), p.3634 - 3638, 2017/06

https://doi.org/10.1007/s11664-016-5259-x

被引用回数：3 パーセンタイル：19.84(Engineering, Electrical & Electronic)

A method combining cyclic voltammetry (CV) with X-ray absorption fine structure (XAFS) spectroscopy, viz. CV-XAFS, has been developed to enable in situ real-time investigation of atomic and electronic structures related to electrochemical reactions. We use this method to study the reaction of a Pt/C cathode catalyst in the oxygen reduction reaction (ORR) in an alkaline electrolyte. It was found that the current induced by the ORR was first observed at approximately 0.08 V versus Hg/HgO, although the Pt valence remained almost unchanged. The electronic structure of the catalytic surface in the ORR was observed to be different in the negative and positive scan directions of CV measurements. Hydrogen adsorption is also discussed on the basis of the observation of this spectral change. We have demonstrated that CV-XAFS provides dynamical structural and electronic information related to electrochemical reactions and can be used for in situ real-time measurements of a catalyst.

論文

Study on the deterioration mechanism of layered rock-salt electrodes using epitaxial thin films; Li(Ni, Co, Mn)O $_{2}$ and their Zr-O surface modified electrodes

阿部真知子*; 射場英紀*; 鈴木耕太*; 南嶋宏映*; 平山雅章*; 田村和久; 水木純一郎*; 齋藤智浩*; 幾原雄一*; 菅野了次*

Journal of Power Sources, 345, p.108 - 119, 2017/03

https://doi.org/10.1016/j.jpowsour.2017.01.103

被引用回数：11 パーセンタイル：38.74(Chemistry, Physical)

Ni, Co, Mn三元系リチウムイオン電池正極材料について、その劣化機構について、電気化学測定、X線・中性子線測定により調べた。実験の結果、Ni, Co, Mn三元系正極は、層状岩塩型構造とスピネル構造で構成されており、充放電を繰り返すと、充放電に関与しないスピネル構造が表面を覆っていくことが分かった。一方で、Zr-Oで表面をコートした材料は劣化しないことが知られており、その原因を調べた結果、層状岩塩型構造が安定に存在し続けていることが分かった。さらに、電極/溶液界面のLi濃度を上昇していることも分かった。

論文

Observation of momentum-resolved charge fluctuations proximate to the charge-order phase using resonant inelastic X-ray scattering

吉田雅洋*; 石井賢司; 中惇*; 石原純夫*; Jarrige, I.*; 池内和彦*; 村上洋一*; 工藤一貴*; 小池洋二*; 永田知子*; et al.

Scientific Reports (Internet), 6, p.23611_1 - 23611_8, 2016/03

https://doi.org/10.1038/srep23611

被引用回数：1 パーセンタイル：11.46(Multidisciplinary Sciences)

In strongly correlated electron systems, enhanced fluctuations in the proximity of the ordered states of electronic degrees of freedom often induce anomalous electronic properties such as unconventional superconductivity. While spin fluctuations in the energy-momentum space have been studied widely using inelastic neutron scattering, other degrees of freedom, i.e., charge and orbital, have hardly been explored thus far. Here, we use resonant inelastic X-ray scattering to observe charge fluctuations proximate to the charge-order phase in transition metal oxides. In the two-leg ladder of Sr $_{14-x}$ CaCu $_{24}$ O $_{41}$ , charge fluctuations are enhanced at the propagation vector of the charge order ( $mathbf{q}_mathrm{CO}$ ) when the order is melted by raising the temperature or by doping holes. In contrast, charge fluctuations are observed not only at $mathbf{q}_mathrm{CO}$ but also at other momenta in a geometrically frustrated triangular bilayer lattice of LuFeO. The observed charge fluctuations have a high energy ( 1 eV), suggesting that the Coulomb repulsion between electrons plays an important role in the formation of the charge order.

論文

Negative correlation between electrical response and domain size in a Ti-composition-gradient Pb[(Mg $_{1/3}$ Nb $_{2/3}$ ) $_{1-x}$ Ti $_{x}$ ]O $_{3}$ crystal near the morphotropic phase boundary

清水大輔*; 塚田慎也*; 松浦直人*; 坂本潤哉*; 小島誠治*; 並河一道*; 水木純一郎; 大和田謙二

Physical Review B, 92(17), p.174121_1 - 174121_5, 2015/11

https://doi.org/10.1103/PhysRevB.92.174121

被引用回数：13 パーセンタイル：50.04(Materials Science, Multidisciplinary)

Ti組成が傾斜した単結晶試料Pb[(Mg $_{1/3}$ Nb $_{2/3}$ ) $_{1-x}$ Ti $_{x}$ ]O $_{3}$ を用いてモルフォトロピック相境界(MPB)近傍の相図ならびに電気応答と結晶コヒーレンス長の相関を調べた。結晶は29mol%と34.7mol%付近に相境界がありそれらは単斜晶相MB-単斜晶相MC,単斜晶相MC-正方晶相境界と対応する。結晶コヒーレンス長のTi濃度依存性は電気応答と強い負の相関を示しており、これらはMPB近傍におけるドメインサイズ効果として説明可能である。

論文

Large trigonal-field effect on spin-orbit coupled states in a pyrochlore iridate

植松大介*; 佐賀山基*; 有馬孝尚*; 石川洵*; 中辻知*; 高木英典*; 吉田雅洋*; 水木純一郎; 石井賢司

Physical Review B, 92(9), p.094405_1 - 094405_6, 2015/09

https://doi.org/10.1103/PhysRevB.92.094405

被引用回数：22 パーセンタイル：66.77(Materials Science, Multidisciplinary)

The half-filled topmost valence band of Ir $^{4+}$ in several iridates such as SrIrO, IrO, and CaIrO has been proposed to originate mainly from the spin-orbit coupled $J_{rm eff}=1/2$ states. In pyrochlore iridates IrO (: rare earth), some exotic electronic states are theoretically proposed by assuming $J_{rm eff}=1/2$ states. However, the octahedral coordination around Ir is trigonally distorted, which may affect the energy level scheme of Ir states. Here, we report spectra of resonant elastic and inelastic X-ray scattering in EuIrO at the Ir edges. A large suppression of the magnetic scattering signal at the Ir $L_{rm II}$ edge supports the $J_{rm eff}=1/2$ picture rather than the one. The inelastic scattering spectrum indicates that the magnitude of the trigonal field on the Ir $^{4+}$ states is evaluated to be comparable to the spin-orbit interaction. The energy diagram of the state is proposed based on the simple cluster model.

論文

Interfacial analysis of surface-coated LiMn $_{2}$ O $_{4}$ epitaxial thin film electrode for lithium batteries

鈴木耕太*; 平山雅章*; Kim, K.-S.*; 田港聡*; 田村和久; Son, J.-Y.*; 水木純一郎; 菅野了次*

Journal of the Electrochemical Society, 162(13), p.A7083 - A7090, 2015/08

https://doi.org/10.1149/2.0111513jes

被引用回数：11 パーセンタイル：36.55(Electrochemistry)

LiMn $_{2}$ O $_{4}$ 電極に関して表面コーティングの効果を調べた。SrTiO $_{3}$ (111)基板上に作成した30nm厚のLiMn $_{2}$ O $_{4}$ 薄膜電極上に3nmのLi $_{3}$ PO $_{4}$ をコーティングして電極を作成した。このようにして作成した電極上では、電気化学反応の可逆性が向上することがわかった。これは電極表面がコーティングされていることで、電気化学反応の反応場である界面が安定化されていることを示している。電気化学反応過程における表面構造は、コートしていない場合と比較して変化が少ないことも確認できた。

論文

Towards optimizing the performance of self-regenerating Pt-based perovskite catalysts

Jarrige, I.*; 石井賢司; 松村大樹; 西畑保雄; 吉田雅洋*; 岸浩史*; 谷口昌司*; 上西真里*; 田中裕久*; 笠井秀明*; et al.

ACS Catalysis, 5(2), p.1112 - 1118, 2015/02

https://doi.org/10.1021/cs501608k

被引用回数：18 パーセンタイル：43.96(Chemistry, Physical)

Self-regenerating automotive catalysts owe their remarkable performance to the repeated motion of the precious metal atoms in and out of the perovskite lattice under fluctuating oxidizing and reducing conditions, preventing coalescence of the metal nanoparticles. Here we use resonant inelastic X-ray scattering to characterize the occupied and unoccupied Pt 5d states in two self-regenerating Pt-perovskite catalysts, CaTi $_{0.95}$ Pt $_{0.05}$ O and CaZr $_{0.95}$ Pt $_{0.05}$ O. Upon reduction, the element and symmetry-specific charge excitation spectra reveal a sizeable hybridization between the Pt 5d and the Ti 3d or Zr 4d states at the interface between the nanoparticles and the perovskite, which involves the occupied states and is thus invisible in X-ray absorption spectra. A correlation is found between the strength of this d-band hybridization and the proportion of Pt nanoparticles that remain buried below the surface during reduction, indicating that the motion of the Pt atoms towards the surface is hindered by this hybridization specifically, rather than by the Pt-O bonding. These results provide direct evidence that the strength of the metal-metal d-band hybridization plays a pivotal role in determining the efficiency of self-regeneration in perovskite catalysts.

論文

Mechanistic studies on lithium intercalation in a lithium-rich layered material using Li $_{2}$ RuO $_{3}$ epitaxial film electrodes and surface X-ray analysis

田港聡*; 平山雅章*; 鈴木耕太*; Kim, K.-S.*; Zheng, Y.*; 田村和久; 水木純一郎; 菅野了次*

Journal of Materials Chemistry A, 2(34), p.17875 - 17882, 2014/11

https://doi.org/10.1039/C4TA02795G

被引用回数：21 パーセンタイル：55.49(Chemistry, Physical)

リチウムリッチな層状化合物の表面構造とインターカレーション過程との関係を、X線構造解析手法を用いて調べた。これまでの電気化学測定から、3次元的に拡散するパスがあり、かつ電池容量は、(010)面より(001)面が露出している方が大きいことが分かっている。このことについて、X線回折やXAFS測定により電極表面構造の変化を追跡した結果、(010)面の構造変化は不可逆である一方、(001)面の構造変化は可逆であることが分かった。

論文

Spin-orbit coupling induced semi-metallic state in the 1/3 hole-doped hyper-kagome NaIrO

高山知弘*; Yaresko, A.*; 松本章代*; Nuss, J.*; 石井賢司; 吉田雅洋*; 水木純一郎; 高木英典*

Scientific Reports (Internet), 4, p.6818_1 - 6818_6, 2014/10

https://doi.org/10.1038/srep06818

被引用回数：31 パーセンタイル：81.59(Multidisciplinary Sciences)

The complex iridium oxide NaIrO with a B-site ordered spinel structure was synthesized in single crystalline form, where the chiral hyper-kagome lattice of Irions, as observed in the spin-liquid candidate NaIrO, was identified. The average valence of Ir is 4.33+ and, therefore, NaIrO can be viewed as a doped analogue of the hyper-kagome spin liquid with Ir $^{4+}$ . The transport measurements, combined with the electronic structure calculations, indicate that the ground state of NaIrO is a low carrier density semi-metal. We argue that the semi-metallic state is produced by a competition of the molecular orbital splitting of $t_{2g}$ orbitals on Ir triangles with strong spin-orbit coupling inherent to heavy Ir ions.

論文

Heterophase fluctuations near $T_{rm c}$ in the relaxor ferroelectrics (1-x)Pb(Zn $_{1/3}$ Nb $_{2/3}$ )O $_{3}$ -xPbTiO $_{3}$ ( = 0.09) studied by X-ray diffuse scattering and coherent X-ray scattering

大和田謙二; 水木純一郎*; 松下三芳*; 並河一道*

Physical Review B, 90(10), p.104109_1 - 104109_12, 2014/09

https://doi.org/10.1103/PhysRevB.90.104109

被引用回数：6 パーセンタイル：28.17(Materials Science, Multidisciplinary)

X線散漫散乱法とコヒーレントX線散乱法を相補利用し、リラクサー強誘電体91%Pb(Zn $_{1/3}$ Nb $_{2/3}$ )O $_{3}$ -9%PbTiO $_{3}$ の強誘電相転移(455K)を調べ、その近傍でヘテロ相ゆらぎが発生していることを明らかにした。ヘテロ相ゆらぎは強誘電相転移(1次相転移)の前駆現象であるばかりでなく、低周波誘電応答の起源とも考えられる。

論文

High-energy spin and charge excitations in electron-doped copper oxide superconductors

石井賢司; 藤田全基*; 佐々木隆了*; Minola, M.*; Dellea, G.*; Mazzoli, C.*; Kummer, K.*; Ghiringhelli, G.*; Braicovich, L.*; 遠山貴己*; et al.

Nature Communications (Internet), 5, p.3714_1 - 3714_8, 2014/04

https://doi.org/10.1038/ncomms4714

被引用回数：89 パーセンタイル：94.27(Multidisciplinary Sciences)

We combine X-ray and neutron inelastic scattering measurements to track the doping dependence of both spin and charge excitations in electron-doped materials. Copper resonant inelastic X-ray scattering spectra show that magnetic excitations shift to higher energy upon doping. Their dispersion becomes steeper near the magnetic zone center and they deeply mix with charge excitations, indicating that electrons acquire a highly itinerant character in the doped metallic state. Moreover, above the magnetic excitations, an additional dispersing feature is observed near the -point, and we ascribe it to particle-hole charge excitations. These properties are in stark contrast with the more localized spin-excitations (paramagnons) recently observed in hole-doped compounds even at high doping-levels.

論文

Bipartite magnetic parent phases in the iron oxypnictide superconductor

平石雅俊*; 飯村壮史*; 小嶋健児*; 山浦淳一*; 平賀晴弘*; 池田一貴*; Miao, P.*; 石川喜久*; 鳥居周輝*; 宮崎正範*; et al.

Nature Physics, 10(4), p.300 - 303, 2014/04

https://doi.org/10.1038/nphys2906

被引用回数：103 パーセンタイル：95.46(Physics, Multidisciplinary)

High-temperature (high- $T_{rm c}$ ) superconductivity appears as a consequence of the carrier-doping of an undoped parent compound exhibiting antiferromagnetic order; thereby, ground-state properties of the parent compound are closely relevant to the superconducting state. On the basis of the concept, a spin-fluctuation has been addressed as an origin of pairing of the superconducting electrons in cuprates. Whereas, there is growing interest in the pairing mechanism such as an unconventional spin-fluctuation or an advanced orbital-fluctuation due to the characteristic multi-orbital system in iron-pnictides. Here, we report the discovery of an antiferromagnetic order as well as a unique structural transition in electron-overdoped LaFeAsO $_{1-x}$ H (), whereby another parent phase was uncovered, albeit heavily doped. The unprecedented two-dome superconducting phases observed in this material can be interpreted as a consequence of the carrier-doping starting from the original at and advanced at parent phases toward the intermediate region. The bipartite parent phases with distinct physical properties in the second magnetic phase provide us with an interesting example to illustrate the intimate interplay among the magnetic interaction, structural change and orbital degree of freedom in iron-pnictides.

論文

Momentum-resolved resonant inelastic X-ray scattering on a single crystal under high pressure

吉田雅洋*; 石井賢司; Jarrige, I.*; 綿貫徹; 工藤一貴*; 小池洋二*; 熊谷健一*; 平岡望*; 石井啓文*; Tsuei, K.-D.*; et al.

Journal of Synchrotron Radiation, 21(1), p.131 - 135, 2014/01

https://doi.org/10.1107/S1600577513028944

被引用回数：3 パーセンタイル：19.04(Instruments & Instrumentation)

A single-crystal momentum-resolved resonant inelastic X-ray scattering (RIXS) experiment under high pressure using an originally designed diamond anvil cell (DAC) is reported. The diamond-in/diamond-out geometry was adopted with both the incident and scattered beams passing through a 1 mm-thick diamond. This enabled us to cover wide momentum space keeping the scattering angle condition near 90 $^{circ}$ . Elastic and inelastic scattering from the diamond was drastically reduced using a pinhole placed after the DAC. Measurement of the momentum-resolved RIXS spectra of Sr $_{2.5}$ Ca $_{11.5}$ Cu $_{24}$ O $_{41}$ at the Cu -edge was thus successful. Though the inelastic intensity becomes weaker by two orders than the ambient pressure, RIXS spectra both at the center and the edge of the Brillouin zone were obtained at 3 GPa and low-energy electronic excitations of the cuprate were found to change with pressure.

論文

Instrumental upgrades of the RIXS spectrometer at BL11XU at SPring-8

石井賢司; Jarrige, I.*; 吉田雅洋*; 池内和彦*; 稲見俊哉; 村上洋一*; 水木純一郎

Journal of Electron Spectroscopy and Related Phenomena, 188, p.127 - 132, 2013/06

https://doi.org/10.1016/j.elspec.2012.12.003

被引用回数：13 パーセンタイル：59.51(Spectroscopy)

Two recent instrumental upgrades of the inelastic X-ray scattering spectrometer installed at BL11XU at SPring-8 are reported. The first one is a multianalyzer system, where we can simultaneously use three crystal analyzers aligned perpendicularly to the scattering plane. In a test measurement of polycrystalline -PtO, the inelastic spectra obtained with each respective analyzer showed a completely identical lineshape, and a slight difference ( 10%) in intensity. The system enhances the experimental efficiency, and allows for simultaneous scan at three momenta for a single-crystal sample. The second development is a polarization analyzer for the scattered photons. A pyrolytic graphite (PG) crystal is placed in front of the detector and serves as a polarization-analyzer crystal, using the (006) reflection for the Cu -edge. We succeeded to observe clear polarization dependence in the - excitations of KCuF.