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Effects of magnetic impurity on the superconductivity has been investigated in Mg1-xMnB2. With increase of Mn concentration x, the lattice constant c (perpendicular to the boron sheet) decreases at a rate of -1.4 % (= dlnc/dx), while a remains nearly unchanged. The transition temperature Tc steeply decreases with $x$ at a rate of dTc/dx = - 159 K. These results suggest that superconducting state of the parent MgB2 is amenable to the magnetic impurities, i.e., Mn2+., Comment: 2 pages, 5 figure

The atomic displacement involved in the crystal structure of the ferromagnetic insulating phase in La1−xSrxMnO3 has been reexamined by transmission electron microscopy, using a x=0.15 single crystal. An analysis of the electron diffraction patterns taken from the x=0.15 samples showed that the atomic displacement consists of a superposition of the Jahn–Teller displacement with q=〈12 12 0〉C and the inverse Jahn-Teller one with q=〈121/2 14〉C, where the subscript c denotes the cubic Brillouin zone. The crystal structure involving these displacements can be identified as a stripe structure.

We have revealed that a bi-stripe order with the [1 0 0] propagation vector (vertical direction) exists in the A-type antiferromagnetic spin ordered phase in half-doped bilayer manganite LaSr2Mn2O7, which also exhibits the CE-type charge/spin order in the intermediate temperature. Although the CE-type charge order (CO) diminishes at low temperatures, the bistripe order exists over a whole temperature. Unlike other half-doped manganites in which the CE-type CO controls the transport properties, the bi-stripe order is responsible for the insulating behavior of the resistivity in LaSr2Mn2O7. Thereby, the picture of phase separation between the metallic region and the CE-type charge/orbital ordered insulating region is not valid in the LaSr2Mn2O7 system.

The charge ordering in the bilayer manganite system La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ with $0.30 \le x \le 0.50$ has been studied by neutron diffraction. The charge order is characterized by the propagation vector parallel to the [1 0 0] direction (MnO$_2$ direction), but the correlation length is short-ranged and extremely anisotropic, being $\sim 0.02a^{*}$ and $\sim 0.2a^{*}$ parallel and perpendicular to the modulation direction, respectively. The observed charge order can be viewed as a quasi-bi-stripe order, and accounts well for the $x$ dependence of the resistivity. The quasi-bistripe order is stable within the ferromagnetic (FM) MnO$_2$ layers in the A-type antiferromagnetic order, but is instabilized by the 3 dimensional FM order., 11 pages, 5 figures

Temperature variation of resistivity and specific heat have been measured for prototypical half-metallic ferromagnets, R_0.6Sr_0.4MnO_3, with controlling the one-electron bandwidth W. We have found variation of the temperature scalings in the resistivity from T^2 (R = La, and Nd) to T^3 (R = Sm), and have interpreted the $T^3-law in terms of the anomalous single-magnon scattering (AMS) process in the half-metallic system., To appear in Phys. Rev. Lett., 3 pages + 4 EPS figures

Low temperature resistivity of CMR manganites is investigated. At the ground state, conduction electrons are perfectly spin polarized, which is called half-metallic. From one-magnon scattering processes, it is discussed that the resistivity of a half metal as a function of temperature scales as rho(T) - rho(0) propto T^3. We take (Nd,Tb,Sr)MnO_3 as an example to compare theory and experiments. The result is in a good agreement., Comment: To appear in Proc. ICM 2000

Optical reflectivity spectra were measured on cleaved surfaces of La1-xSrxMnO3 single crystals (x=0.175, T_C=283 K) over a temperature range 10-295 K. The optical conductivity $sigma(\omega)$ shows, keeping single-component nature, incoherent-to-coherent crossover with increase of electrical conductivity. The $\sigma(\omega)$ spectrum of low-temperature ferromagnetic-metallic phase (10 K) exhibits a pronounced Drude-like component with large spectral weight, contrary to the previous result. The present result indicates that the optical spectrum of the manganites is sensitive to condition of sample surfaces., Comment: 6 pages, 3 figures, to be published in Physica Status Soloidi (b) (proceedings of ICSSS'99)

Inelastic neutron-scattering measurements were performed on a single crystal of the layered colossal magnetoresistance (CMR) material La1.2Sr1.8Mn2O7 (Tc ~ 120K). We found that the spin wave dispersion is almost perfectly two-dimensional with the in-plane spin stiffness constant D ~ 151meVA. The value is similar to that of similarly doped La1-xSrxMnO3 though its Tc is three times higher, indicating a large renormalization due to low dimensionality. There exist two branches due to a coupling between layers within a double-layer. The out-of-plane coupling is about 30% of the in-plane coupling though the Mn-O bond lengths are similar., 3 pages, 3 figures J. Phys. Chem. Solids in press

Systematic powder diffraction studies have been carried out to establish the magnetic phase diagram of La_{2-2x}Sr_{1+2x}Mn_2O_7 (LSMO327) in a wide hall concentration range ($0.30 \leq x \leq 0.50$), using the HERMES diffractometer. LSMO327 exhibits a planar ferromagnetic structure for $0.32\leq x\leq 0.38$ at low temperatures. A finite canting angle between planar magnetic moments on neighboring planes starts appearing around $x\sim 0.40$ and reaches 180$^{\circ}$ (A-type antiferromagnet) at x=0.48. At x=0.30, on the other hand, the magnetic moments are aligned parallel to the c-axis., Comment: 3 pages, 3 figures J. Phys. Chem. Solids in press

A Raman-scattering investigation of the double-layer manganites. La2−2xSr1+2xMn2O7 (x=0.4,0.5), revealed signatures of a) charge stripe formation and melting, b) small polaron formation, and c) anisotropic quasiparticle dynamics in the ferromagnetic-metallic state. These observations and their implications are discussed in this work.

We investigated optical properties of Pr_{0.5}Sr_{0.5}MnO_3, which has the A-type antiferromagnetic ordering at a low temperature. We found that T- dependence of spectral weight transfer shows a clear correlation with the magnetic phase transition. In comparison with the optical conductivity results of Nd_{0.5}Sr_{0.5}MnO_3, which has the CE-type antiferromagnetic charge ordering, we showed that optical properties of Pr_{0.5}Sr_{0.5}MnO_3 near the Neel temperature could be explained by a crossover from 3D to 2D metals. Details of spectral weight changes are consistent with the polaron picture., Comment: 11 pages, 4 figures, submitted to PRL at June 1

Soft X-ray magnetic circular dichroism (SXMCD) measurements are reported on the O K- and Mn L-absorption edges of La1-xSrxMnO3 (x = 0.15, 0.18, and 0.4) single crystals in their ferromagnetic regime. This has been done using a recently developed experimental technique for magnetizing the samples offering the possibility to get high-accuracy SXMCD effect measurements on bulk samples. The very strong doping-induced O K-edge intensity is proof of an enhanced O 2p hole component of the doped holes. O K soft X-ray magnetic circular dichroism spectra give evidence for an orbital magnetic moment of this O 2p component ferromagnetically coupled to the Mn moments. (C) 1997 Elsevier Science B.V.

We have performed X-ray absorption (XAS) and angle-resolved photoemission (ARPES) on single crystals of both the layered and cubic colossal magnetoresistive manganites to determine the electronic structure and the relevant energy scales in the problem: the intra-atomic exchange energy J (∼ 2.7 eV), the Jahn-Teller energy gain EJ-T (W (>3 eV for layered compounds) and the lattice relaxation or polaron binding energy EB (.65 eV ferromagnetic phase and.8 eV paramagnetic phase). Lattice polarons are deemed important especially in the paramagnetic but also to a degree in the ferromagnetic phase. Due to the energy scale mismatch, the Jahn-Teller effect is unlikely to be the cause for these lattice polarons, at least for the layered samples.

We have studied the fc-dependent electronic structure of the layered colossal magnetoresistive manganite La1.2Sr1.8Mn2O7 using high-resolution angle-resolved photoemission spectroscopy. We found dispersive energy bands as a function of the crystal momentum k near the Fermi level (EF). We have also performed local spin density approximation (LSDA)+U band-structure calculations on the current system. The overall experimental dispersion relation is basically in agreement with the band-structure calculations yet close to EF there is a significant deviation from the predicted dispersions. Instead of clear Fermi-surface (FS) crossings, we observe a depression of the features as the FS is approached as if there is a “pseudo” gap in the excitation spectrum. The pseudogap continuously opens with temperature and does not show further significant opening above Tc, corresponding to the metal-insulator transition. Those unusual aspects of the spectra has been discussed from the viewpoint of the strong electron-lattice coupling model.

P2-type NaxMO2 (M = Mn and Co) with a layered structure is a promising cathode material for low-cost sodium ion secondary batteries (SIBs). Here, we performed an in situ X-ray absorption spectroscopy (XAS) of NaxMnO2 and NaxCoO2 near the Mn and Co K-edges against Na concentration (x). In both compounds, the red shift of the main peak with x indicates the electron doping on the Mn 3d (Co 3d) orbital. We further analyzed the pre-edge XAS profiles with several configuration models. In NaxMnO2, the spectral weights of the doublet components suggest the high-spin (HS) state of Mn. In NaxCoO2, the single peak feature suggests that the ground-state configurations of Co4+ and Co3+ have significant weights of d6L and d7L, where L denotes an oxygen 2p hole.

By means of femto-second time-resolved spectroscopy, we investigated the carrier formation process against film morphology and temperature (T) in highly-efficient organic photovoltaic, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b] thiophenediyl]] (PTB7)/[6,6]-phenyl C71-butyric acid methyl ester (PC70BM) solar cells. We found that the carrier formation efficiency (ϕCF) from an absorbed photon is nearly independent of the film morphology, indicating that the internal quantum efficiency (ϕIQ) is mainly governed by the carrier transfer efficiency (ϕCT) to the electrodes. The activation energy (Ea=0.5–0.8 meV) of ϕCF is significantly low, which suggests an extended charge-transfer state around the PTB7/PC70BM interface.

The temperature dependence of sodium ion diffusion coefficient (D) of NaxCoO2 is extensively investigated in the temperature range of 303≤T≤349 K using electrochemical impedance spectroscopy. The magnitude of D is found to be (0.7–1.9)×10-11 cm2/s (0.54≤x≤0.85) at 303 K, which is comparable to that of LiCoO2. The activation energy (EaD) of D gradually increases from 0.32 at x=0.54 to 0.51 eV at x=0.85. The activation energy (EaR) of charge-transfer resistance (Rct) also increases from 0.34 at x=0.54 to 0.59 eV at x=0.85. These behaviors are ascribed to an increase in potential barrier due to the decrease in interlayer distance (d).

P2-type NaxMnO2 (P63/mmc, Z = 2) with a layered rock-salt structure is a promising cathode material for low-cost sodium ion secondary batteries (SIBs). Here, we performed an ex situ synchrotron radiation x-ray structural analysis of NaxMnO2 (0.43 ≤x ≤0.71) against Na+ concentration (x). We found that the thicknesses (dNaO2) of the NaO2 layer is nearly independent of x, in a sharp contrast to the rapid decrease observed in isostructural NaxCoO2. In addition, the site energy differences [Δe= e1 - e2; e1 (e2) is the site energy at Na1 (Na2)] in NaxMnO2 are much smaller than those in NaxCoO2. These observations are interpreted in terms of the screening effect of the Na+ charge in NaxMnO2.

Electronic state of cobalt and manganese Prussian blue analogues were systematically investigated against Na+ intercalation by means of the infrared and X-ray absorption spectroscopies. The spectroscopies revealed that 3.8 and 3.4 V plateaus in the discharge curve of Na x Co[Fe(CN)6]0.902.9H2O (denoted as NCF90) are ascribed to the reduction processes of Fe3+ and Co3+, respectively. On the other hand, 3.6 and 3.2 V plateaus of Na x Mn[Fe(CN)6]0.833.5H2O (NMF83) are ascribed to the reduction processes of Mn3+ and Fe3+, respectively. We found that the film electrodes with a thickness of 1.1 µm exhibit fast Na+ intercalations: the discharge capacity at 60 C of the NCF90 (NFM83) film was 90% (45%) of the open-circuit-voltage (OCV) value. Thus, Prussian blue analogue films are promising cathode candidates for sodium-ion secondary batteries.

We performed femtosecond time-resolved spectroscopy in α-sexithiophene (6T)/C60 bilayer and mixed films. We observed sharp and intense photoinduced absorption (PIA) at 1.2 eV and ascribed it to the charge-transfer (CT) state. The spectral features are interpreted in terms of homogenous molecular stacking at 6T/C60 interface and quantum confinement effect in 6T.

A bulk heterojunction (BHJ) based on a donor (D) polymer and an acceptor (A) fullerene derivative is a promising organic photovoltaic (OPV). We investigated femtosecond charge dynamics after D (at 633 nm) and A (at 400 nm) excitations in a prototypical low-band-gap and highly efficient OPV, i.e., poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7)/[6,6]-phenyl C71-butyric acid methyl ester (PC70BM). The photoinduced absorption (PIA) spectra of the blend film were decomposed into three PIAs, i.e., donor exciton (D*), acceptor exciton (A*), and carrier (D+) components. The analysis revealed that D*→D+ conversion predominates in 633 nm excitation, while A*→D+ conversion predominates in 400 nm excitation. The carrier formation times of both processes are nearly the same (τrise∼0.2–0.3 ps).

We have prepared Li-intercalated LixBi2Sr2CaCu2O8+δ (x =0-2.0) samples by using electrochemical method, and performed synchrotron x-ray diffraction, Cu K-edge x-ray absorption fine structure (XAFS), and magnetic susceptibility measurements. With increasing x, a- and c-lattice parameters monotonically increase, which shows lithium intercalation into Bi2Sr2CaCu2O8+δ. Accompanied by the lithium insertion, the valence of Cu ion changes from Cu2+/Cu3+ to Cu1+/Cu2+ to realize charge neutrality. This change of the valence was detected by Cu K-edge XAFS measurement. A clear increase of spectral weight that corresponds to 1s→ 4pπ(3d10L) was observed at around 8982 eV with x. The superconducting (SC) transition temperature TC significantly changes from 74 K for x = 0 to 90 K for x = 0.8, which is attributed to modified density of states by the decrease of hole concentration. A volume fraction of the superconducting phase was 1-2 % for x ≥ 0.6 implying phase separation where Li-rich non SC phase and Li-poor SC phase coexist. Such a phase separation is universally seen in electrode active materials.

We investigated the electronic states and structural properties of LixMn(Fe(CN)6)0.83·3.5H2O, and LixMn(Fe(CN)6)0.87·2.6H2O, which have different amount of (Fe(CN)6) vacancies. X-ray absorption spectra near the Fe and Mn K-edges revealed that the Li intercalation/deintercalation process is two-electron reaction, i.e. Mn II —NC—Fe II , Mn II — NC—Fe III , and Mn III —NC—Fe III . The crystal structure of LixMn(Fe(CN)6)0.83·3.5H2O remains cubic and single phase throughout the Li intercalation/deintercalation process. The crystal structure of LixMn(Fe(CN)6)0.87·2.6H2O is also cubic, while phase separation of Li + -rich phase and Li + -poor phase was observed during the Mn II /Mn III reduction/oxidation process.

We investigated carrier formation dynamics in a small-molecular bulk heterojunction solar cell, 2,5-di-(2-ethylhexyl)-3,6-bis-(5″-n-hexy-[2,2′,5′,2″]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrolo-1,4-dione/[6,6]-phenyl C71-butyric acid methyl ester, with low bandgap (Egap ≈ 1.5 eV). The photoinduced absorption (PIA) spectra of the blend film were decomposed into three PIAs, i.e., those due to donor exciton (D*), acceptor exciton (A*), and mobile carrier (D+). The analysis revealed carrier conversion from D* with a conversion time of ∼1.3 ps.

Prussian blue analogues with jungle-gym-type structure are promising candidates for cathode materials of the lithium-ion secondary battery (LIB). Here, we investigated the structural, electronic, and electrochemical properties of cobalt hexacyanoferrate, Li x Co[Fe(CN)6]0.902.9H2O, against Li concentration (x). The capacity (= 139 mAh/g) of the thin-film electrode was close to the ideal value (= 132 mAh/g) for the two-electron reaction. The discharge curve exhibits three plateaus, i.e., plateaus I, II, and III. The material exhibits a first-order phase transition accompanied by significant volume expansion by 7% at the boundary between plateaus II and III. Ex situ X-ray absorption spectroscopy (XAS) indicates that the discharge processes of plateaus I, II, and III are ascribed to the reduction processes of Fe3+, Co3+, and Fe3+, respectively. The rate (r) and cycle (n) dependence of the electrode performance will be discussed in terms of the reduction processes.

Electrochemical properties are investigated for thin film electrode of NaxCoO2, which was fabricated by pulsed laser deposition. A high rate of 400 C was realized in the film together with a fine cyclability where its capacity after 1000 cycles remains 84.4% of the initial one. The NaxCoO2 thin film exhibits a clear sign of the structural phase transition induced by Na+ intercalation even at the high rate of 200 C. This observation indicates bulk nature of the rapid and highly-reversible Na+ intercalation in NaxCoO2.

We investigated structural and electrochemical properties of thin film electrodes of cobalt hexacyanoferrate, NaxCo[Fe(CN)6]0.902.9H2O, against x. The compound exhibits a high capacity of 135 mAh/g and an average operating voltage of 3.6 V against Na, with a good cyclability. The discharge curve exhibits two plateaus at ≈3.8 and ≈3.4 V, which are ascribed to the reduction processes of Fe3+ and Co3+, respectively. The ex situ X-ray diffraction (XRD) profiles reveal the robust nature of the host framework against Na+ intercalation/deintercalation. Thus, cobalt hexacyanoferrate is a promising candidate for the cathode material of sodium-ion secondary battery (SIB).

A thin film of sodium manganese ferrocyanide, Na1.32Mn[Fe(CN)6]0.83·3.5H2O, exhibits discharge capacity (= 109 mA h g(-1)) and discharge voltage (3.4 V in average) at 0.5 C against Na in aprotic solvent. The ex situ XRD experiments reveal that the host framework remains cubic without showing any structural phase transition during the charge process. The discharge property is discernible up to 40 C.

The electronic structures of Mo-based pyrochlore oxides of R2Mo2O7 (R= Nd, Sm) have been investigated by using photoemission spectroscopy. The electronic states near EF are found to have mainly Mo 4d character, and they are not affected much by R 4f states located well below EF. The origin of the stable ferromagnetic phase in Nd2Mo2O7 is discussed in terms of the kinetic energy optimization.

Neutron scattering studies on a single crystal of the highly-correlated electron system, La1-xSrxMnO3 with x~0.3, have been carried out elucidating both the spin and lattice dynamics of this metallic ferromagnet. We report a large measured value of the spin wave stiffness constant, which directly shows that the electron transfer energy of the d band is large. The spin dynamics, including magnetic critical scattering, demonstrate that this material behaves similar to other typical metallic ferromagnets such as Fe or Ni. The crystal structure is rhombohedral, as previously reported, for all temperatures studied (below ~425K). We have observed new superlattice peaks which show that the primary rhombohedral lattice distortion arises from oxygen octahedra rotations resulting in an R-3c structure. The superlattice reflection intensities which are very sensitive to structural changes are independent of temperature demonstrating that there is no primary lattice distortion anomaly at the magnetic transition temperature, Tc = 378.1 K, however there is a lattice contraction., Submitted to Phys. Rev. B. (03Aug95) Uuencoded gz-compressed .tar file of Postscript text (12 pages) and 6 figures. Also available by WWW from http://insti.physics.sunysb.edu/~mmartin/ under my list of publications or by e-mail request

We have synthesized the [Fe(II)(Htrz) 3 ] complex film by using ion-exchange film (Nafion) as counter anion. From the analysis of Fe Kedge EXAFS spectra, we could prove the existence of one-dimensional Fe chain structure, [Fe(II)(Htrz) 3 ] n on Nafion film. [Fe(II)(Htrz) 3 ]-Nafion showed a spin crossover phenomenon around room temperature. Moreover, the LIESST(Light Induced Spin State Trapping) effect was observed at 4.2 K.

In RbMn[Fe(CN)6], 1,2) two kinds of magnetic elements, i.e., Fe and Mn, form a three-dimensional NaCl-type structure bridged by CN ions. Recently, Tokoro et al. has reported suppression of magnetization by irradiation of one-pulse laser shot (532 nm, 10mJ cm ) at 3 K. This observation suggests photo-induced ferromagnetic-to-antiferromagnetic transition, perhaps mediated by some photoinduced structural change. To clarify this novel photoinduced phenomenon, we first have to determine the spin structure of the ground state (before photo-irradiation). Crytallographically, RbMn[Fe(CN)6] belongs to the tetragonal space group (I4m2; Z 1⁄4 2) at low temperatures, in which Fe and Mn elements locate at 2a and 2b site, respectively. The low temperature valence state is considered to be high-spin Mn3þ (d; S 1⁄4 2) and low-spin Fe2þ (d; S 1⁄4 0) state. In this Note, we report the spin structure of RbMn[Fe(CN)6] determined by neutron powder diffraction by the Kinken powder diffractometer for high efficiency and high resolution measurements (HERMES). The observed magnetic Bragg reflection pattern is well reproduced by ferromagnetic alignment of the Mn3þ local spins along c. The Curie temperature is determined to be TC 1⁄4 13ð1ÞK. We will discuss a possible origin for the ferromagnetic coupling between the Mn3þ local spins. RbMn[Fe(CN)6] was prepared by reacting an aqueous solution (0.1mol dm ) of MnCl2 with a mixed aqueous solution of RbCl (1mol dm ) and K3[Fe(CN)6] (0.1mol dm ) to yield a light brown precipitate. With use of a SQUID magnetometer, we have measured temperature variation of magnetization M under a field of 10G. TheM{T curve increases steeply below 12K. The saturated magnetization is 3:3 B (at 7 T) at 3K. Neutron powder diffraction measurements were performed using the Kinken powder diffractometer for high efficiency and high-resolution measurements (HERMES) of Institute for Materials Research, Tohoku University, installed at the JRR-3M reactor at the Japan Atomic Energy Research Institute, Tokai, Japan. Neutrons with wavelength 1.8207 A were obtained by the (331) reflection of the Ge monochromator, and 120-B-Sample-180 collimation. The RbMn[Fe(CN)6] powders ( 1 g) sealed in a vanadium capsule (9mm ) with helium gas, and mounted at the cold head of a closed-cycle He-gas refrigerator. The diffraction data were integrated for 3 h. First, we investigated the lattice structure at 20K by Rietveld structural analysis (RIETAN2000) with the same model as ref. 4. Reflecting the Jahn–Teller instability of the Mn3þ (d) ions, the MnN6 octahedra are elongated along c: the Mn–N1 (out-of-plane) and Mn–N2 (in-plane) bond distances are 2.1997(37) A and 1.9581(29) A, respectively. On the other hand, distortion of FeC6 octahedra is much smaller: the Fe–C1 (out-of-plane) and Fe–C2 (in-plane) bond distances are 1.8868(42) A and 1.9167(58) A, respectively. Figure 1(a) shows neutron powder patterns at 5K ( TC; thick curve) and at 20K ( TC: thin curve) for RbMn[Fe(CN)6]. In the middle panel [Fig. 1(b)], we show magnetic components of the neutron powder pattern. Several magnetic Bragg reflections are observed at 18 , 21 , 29 and 35 . No trace of (002) magnetic Bragg reflection is observed, indicating that the easy axis is along c. This is consistent with the elongation of the MnN6 octahedra along c. In the Bottom panel [Fig. 1(c)], we plotted calculated intensities IM,cal of the magnetic Bragg reflections with ferromagnetic alignment of the Mn3þ local spins along c. IM,cal is expressed as IM.cal / mhkl Lð Þ jFMðQÞj; ð1Þ

The tetrahedral geometry in the spinel B site forms the pyrochlore network, which consists of corner-linked arrays of tetrahedral plaquettes. If the B–B exchange coupling is antiferromagetic and the spin direction is collinear, the pyrochlore lattice leads to intense frustration of the magnetic bonds. Among the transition metal spinel, Mn3O4 has a tetragonal (I41=amd; Z 1⁄4 4) structure due to the Jahn–Teller instability of Mn3þ (d) at the B site (octahedral site). Such a lattice distortion is advantageous for a collinear spin arrangement of the spinel B lattice. This compound shows a magnetic transition into the spin ordered phase at Tc 1⁄4 41K. Jensen and Nielsen have performed magnetic structural analysis on single crystalline Mn3O4 and reported a rather complicated spin structure with the two-fold periodicity along b. The A-spins (Mn2þ) are ferromagnetically ordered along b. On the other hands, the B-spins (Mn3þ) align nearly along c reflecting the Jahn–Teller distortion of the MnO6 octahedra. The B-spin chains along a and b are antiferromagnetically ordered. The B–B antiferromagnetic exchange coupling is considered to be stronger than the A–B exchange coupling, since the Mn2þ (d) at the A-site is electronically stable. Then, the B-site pyrocholre lattice is amenable to the geometrical frustration in the paramagnetic phase ( Tc) where the long-range spin order disappears. Neutron powder diffraction measurements were performed using the Kinken powder diffractometer for high efficiency and high resolution measurements (HERMES) of Institute for Materials Research, Tohoku University, installed at the JRR-3M reactor at the Japan Atomic Energy Research Institute, Tokai, Japan. Experimental details were described elsewhere. Powders of Mn3O4 were sealed in a vanadium capsule (10mm ) with helium gas, and mounted at the cold head of a closed-cycle He-gas refrigerator. The powder patterns are measured in the temperature range of 7K T 300K. We performed the Rietveld analysis (RIETAN2000 program) on the powder pattern at 300K (see Table I). Figure 1 shows temperature variation of neutron powder patterns in the small-2 region. At the lowest temperature (7K Tc), intense (101) magnetic Bragg reflection (indicated by a downward arrow) is observed at 21 . [The (101) reflection in the tetragonal setting corresponds to the (111) reflection in the cubic spinel.] With increase of temperature, a broad diffuse scattering (hatched region) appears at 20 . Trace of the scattering is detectable even at 300K ( Tc 1⁄4 41:9K). This diffuse scattering can be ascribed to the short-range spin correlation on the B-site pyrochlore lattice, because the scattering extends around the (101) magnetic Bragg reflection. Existence of the short-range correlation of the B-spins is also supported by the specific heat measurements. We measured specific heat of a meltgrown Mn3O4 crystal with use of Quantum Design PPMS machine. We observed -type anomaly at Tc (not shown), and estimated the spin entropy change S ( 2:2kB/ Mn3O4) at Tc. Magnitude of S is roughly consistent with the previous report [2:6ð1ÞkB/Mn3O4]. Here, S is much smaller than the ideal value [2 ln 5þ ln 6 ð 5:0ÞkB/Mn3O4], and is rather close to the A-spin contribution to the entropy change [ln 6 ð 1:8ÞkB/Mn3O4]. Table I. Refined structural parameters of Mn3O4 at 300K, determined by Rietveld analysis of neutron powder patterns. The crystal symmetry is tetragonal (I41=amd; Z 1⁄4 4). The lattice constants are a 1⁄4 5:7602ð2Þ A and c 1⁄4 9:4602ð4Þ A. g and B are the occupancy and isotropic atomic thermal parameter, respectively. Rwp ( 1⁄2 iwiðyi yi;calcÞ 2 iwiy 2 i ) and RI ( K jIK;calc IK j K IK;calc ) are 9.48% and 3.86%, respectively.

Manganese hexacyanoferrate, La x Mn[Fe(CN)6] y zH2O, is a promising candidate for cathode materials for lithium ion secondary batteries, because the compound exhibits an ideal two-electron reaction without structural phase transition at y =0.83. We found that its capacity (Q) increases with Fe concentration (y) from Q = 115 mAh/g at y = 0.83 to 130 mAh/g at 0.87, and 143 mAh/g at 0.93. We further investigated the structural properties of La x Mn[Fe(CN)6] y zH2O against the Li concentration (x). In the low-x region, the y = 0.87 compound exhibits a phase separation into the two cubic phases, whereas the y = 0.93 compound separates into the cubic and tetragonal phases. We ascribed these phase separations to the Jahn–Teller (JT) instability as well as the smaller ionic radius of Mn3+.

The thickness (L) dependence of the discharge curve is systematically investigated for a thin-film electrode of a polymer-type cathode material, Li x Mn[Fe(CN)6]0.81·3.0H2O. We realized an extremely high discharge rate at 3000 C (= 4 mA/cm2) with high capacity (= 85 mAh/g) as well as good cyclability (no reduction was observed after 30 cycles) at L = 0.12 µm. We derived interrelation between the discharge time (T) and the film thickness (L), and interpreted the relation in terms of the one-dimensional (1D) Li+ diffusion process. We ascribed the fast discharge process to the large Li+ diffusion constant (D) as well as the ideal electric contact between the collective electrode and the active material.

Charge formation on the donor–acceptor (D–A) interface is the key process in organic photovoltaics (OPVs). Here, we experimentally demonstrated that the charge formation dynamics in the hexabenzocoronene (HBC)–C60 dyad system crucially depends on the structure of the D–A interface. In the self-assembled (SA) film with well-defined tube-type interface, we observed a conversion process from the donor HBC exciton (D*) to the donor charge (D+). Reflecting the two-dimensional (2D) shape of the respective domains, the charge formation time (τrise = 7.9 ps) in the SA film is much slower than τrise (≤1 ps) in the nonassembled (NA) film.

We demonstrated that divalent manganese/zinc ions (MnII/ZnII) and ferricyan ion [FeIII(CN)6]3- cooperatively trap the cesium ion in aqueous solution within the self-fabricated cubic nanospace with high efficiency. In the low-Cs+-concentration region (≤100 ppm), addition of 5 mmol/L [Fe(CN)6]3+ and 5 mmol/L MnII/ZnII significantly reduces the Cs+ concentration 0.003/0.008 ppm. In the higher-concentration region, the Cs trapping capacity (T≡MCs/Mhost, where MCs and Mhost are the masses of the trapped cesium and host, respectively) reaches T = 420/410 mg/g above 6 mmol/L. The size matching between the nanospace (5.30/5.20 A for the Mn/Zn compounds, respectively) and the ionic radius (rCs+ = 1.74 A) of the guest Cs+ is responsible for the high trapping efficiency.

Bulk heterojunction (BHJ) based on a donor (D) polymer and an acceptor (A) fullerene derivative is a promising organic photovoltaic. Here, we investigated the femtosecond charge dynamics after acceptor excitation in poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b '] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b] thiophenediyl]] (PTB7)/[6,6]-phenyl C71-butyric acid methyl ester (PC70BM), which is a low-gap (Egap≈1.6 eV) organic photovoltaic. We observed fast conversion from the acceptor exciton (A*) to the donor polaron (D+) within τrise = 0.45 ps. The fast carrier formation is ascribed to the prompt charge transfer of an electron from the D highest occupied molecular orbital (HOMO) to the A HOMO.

A new class of electrode materials are being intensively investigated to achieve a low-cost Li+ secondary battery (LIB) with a high discharge rate. Here, we investigated the discharge rate in thin film electrodes of the Prussian blue analogues (Li,Na)4y-2M[Fe(CN)6]yzH2O (M =Ni, Co, Mn, and Cd). Except for the Co compound, the capacities at 100 C exceed 60% of those at 1 C. We further investigated the electronic and crystal structures of Prussian blue analogues against Li+ concentration (x). On the basis of these data, we will discuss the origin of the rapid Li+ intercalation.

We have fabricated an oxide thermal rectifier made of La1.98Nd0.02CuO4 and MnV2O4. By utilizing a jump of a thermal conductivity originated in the structural phase transition accompanied by the orbital ordering in MnV2O4, a rectifying coefficient of 1.14 has been achieved in the presence of a small temperature difference of 2 K. A thermal rectifier operating under a small temperature difference will play an important role for realizing heat-current control in electronic devices.

We found that the alignments of the alkali cations can be controlled by a distortion of Prussian blue framework; the rubidium ions form a rod structure in a distorted framework of Rb(0.85)Cu[Fe(CN)(6)](0.95)·1.3H(2)O, while the cesium ions are isolated dot structures in a non-distorted framework of Cs(0.97)Cu[Fe(CN)(6)](0.99)·1.1H(2)O. The Madelung energy calculations revealed that the novel rod structure is stabilized by the alternating rotations of the [Fe(CN)(6)] units within the three-dimensional coordination polymer framework.

Dept. of Crystalline Materials Science, Nagoya University, Nagoya 464-8603 Dept. of Applied Physics, Nagoya University, Nagoya 464-8603 SPring-8/JASRI, 1-1-1 Koto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198 Faculty of Science and Technology, Science University of Tokyo, Chiba 278-8510 ISSP, University of Tokyo, Kashiwa 277-8581 Dept. of Physics, Saitama University, Saitama 338-8570 SPring-8/JAERI, 1-1-1 Koto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198

We performed neutron-diffraction measurements on single crystals of La2-2xSr1+2xMn2O7. For x=0.45, in an intermediate phase (TC

In perovskite-type doped manganites, the phase separation phenomenon is considered to be a probable candidate for the origin of the colossal magnetoresistance effect. This is because the magnetresistance effect is enhanced in the vicinity of the ferromagnetic metallic — charge-ordered insulating phase boundary, where the phase separation effect is also enhanced. Machida et al., however, experimentally indicated that the phase separation of Nd0:55(Sr,Ca)0:45MnO3 takes place at higher temperature ( 200K) than the insulator-metal transition temperature at 150K, and the mass fraction of the insulating phase monotonously increases with further decreases of temperature. This observation indicates that the phase separation has no direct connection with the insulator-metal behavior. Then, the remaining problem is the origin for the lowtemperature phase separation of the perovskite manganites. In this paper, we briefly report structural properties of single-layered manganites, Nd1 xSr1þxMnO4 (0:3 x 0:95). This compound begins to attract current interest due to the rich phase diagram. We found that the compound consists of two single-layered phases even at room temperature in the concentration range of 0:75 x 0:95, probably due to the spinodal decomposition with the Sr2þ concentration as the order parameter. We will compare the present spinodal decomposition in Nd1 xSr1þxMnO4 with the phase separation observed in the perovskite manganites. The polycrystalline samples were synthesized by solidstate reaction in air. A stoichiometric mixture of commercial Nd2O3, SrCO3, and Mn3O4 powders was well ground and calcined twice at 1350 C for 24 h. Then, the resulting powder was pressed into a disk with a size of 20mm 5mm and sintered at 1350 C for 48 h. The temperature of the sintered pellet was cooled down very slowly ( 50K/h). The neutron powder diffraction profiles were obtained at room temperature, using the Kinken powder diffractometer for high efficiency and high resolution measurements (HERMES) installed at the JRR-3M reactor at the Japan Atomic Energy Research Institute, Tokai, Japan. Neutrons with wavelength 1.8196 A were obtained by the 331 reflection of the Ge monochromator, and 120-B-Sample-220 collimation. The sample pellet was crushed into fine powders and sealed in a vanadium capsule (10mm ). The diffraction data were integrated for 3 h. We have performed Rietveld analysis on the obtained powder patterns with use of the RIETAN2000 program. Figure 1 shows prototypical examples of neutron powder pattern (cross) of Nd1 xSr1þxMnO4 at 300K, together with the Rietveld refinement (solid curve): (a) x 1⁄4 0:6 and (b) x 1⁄4 0:8. At x 1⁄4 0:6 ((a)), the tetragonal model (I4=mmm; Z 1⁄4 2) well reproduced the diffraction patterns in the range of 5 2 150 . The final refinements are satisfactory, in which Rwp and RI (reliable factor based on the integrated intensity) are fairly reduced. This model, however, fails to reproduce the powder patterns for 0:75 x 0:95. We tried several structural models, and finally found that the twophase model with two tetragonal (I4=mmm; Z 1⁄4 2) structures satisfactory reproduces the patterns, as exemplified in Fig. 1(b). Hereafter, we distinguish the two single-layered phases by the lattice constant c, and call then as the ‘long-c’ and ‘short-c’ phases for convenience of the explanation. We summarized in Fig. 2 thus obtained structural parameters of Nd1 xSr1þxMnO4: (a) lattice constants, a and c, (b) Mn–O bondlength d and (c) volume fraction s of the long-c phase. Circles and squares represent the short-c and long-c phases, respectively. With increase of x, c (open symbols) steeply decreases, and then gradually increases above x 0:6. On the other hand, a (filled symbols) remains nearly constant up to x 0:7. These x-dependent features of the lattice constants are similar to the case of La2 2xSr1þ2xMn2O7. 7) In 0:75 x 0:95, the compound consists of two single-layered phases with different lattice constants [see Fig. 2(a)]. In a thermodynamical point of view, the two-phase feature means that Nd1 xSr1þxMnO4 is unstable in 0:75 x 0:95, and decomposes into the Sr2þpoor (short-c phase) and Sr2þ-rich (long-c phase) phases (spinodal decomposition). The bottom panel [Fig. 2(c)] shows the mass fraction s of the long-c phase. s monotonously increases as x increases. The middle panel [Fig. 2(b)] shows Mn–O bondlength d 40 60 80 100 0 5 10