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Multiple transition phenomena in divalent Eu compound EuAl$_4$ with the tetragonal structure were investigated via the single-crystal time-of-flight neutron Laue technique. At 30.0 K below a charge-density-wave (CDW) transition temperature of $T_{\rm CDW}$ = 140 K, superlattice peaks emerge near nuclear Bragg peaks described by an ordering vector $q_{\rm CDW}$=(0 0 ${\delta}_c$) with ${\delta}_c{\sim}$0.19. In contrast, magnetic peaks appear at $q_2 = ({\delta}_2 {\delta}_2 0)$ with ${\delta}_2$ = 0.085 in a magnetic-ordered phase at 13.5 K below $T_{\rm N1}$ = 15.4 K. By further cooling to below $T_{\rm N3}$ = 12.2 K, the magnetic ordering vector changes into $q_1 = ({\delta}_1 0 0)$ with ${\delta}_1$ = 0.17 at 11.5 K and slightly shifts to ${\delta}_1$ = 0.194 at 4.3 K. No distinct change in the magnetic Bragg peak was detected at $T_{\rm N2}$=13.2 K and $T_{\rm N4}$=10.0 K. The structural modulation below $T_{\rm CDW}$ with $q_{\rm CDW}$ is characterized by the absence of the superlattice peak in the (0 0 $l$) axis. As a similar CDW transition was observed in SrAl$_4$, the structural modulation with $q_{\rm CDW}$ could be mainly ascribed to the displacement of Al ions within the tetragonal $ab$-plane. Complex magnetic transitions are in stark contrast to a simple collinear magnetic structure in isovalent EuGa$_4$. This could stem from different electronic structures with the CDW transition between two compounds., Comment: 6 pages, 3 figures, accepted for publication in J. Phys. Soc. Jpn

Magnetism in EuNiIn4 is studied using specific heat, magnetic susceptibility, magnetization, 151Eu Mossbauer spectroscopy, and neutron diffraction experiments. The specific heat exhibited two magne...

The magnetic structure of the intermetallic compound EuGa$_4$ was investigated using single-crystal neutron diffraction with the time-of-flight (TOF) Laue technique on the new diffractometer SENJU at MLF of J-PARC. In spite of high neutron absorption of Eu, a vast number of diffraction spots were observed without isotope enrichment. The magnetic reflections were appeared at the positions with the diffraction indices of $h+k+l{\neq}2n$ below 16 K, indicating that the ordering vector is ${\bf q}=(0~0~0)$. Continuous evolution of magnetic reflection intensity below $T_{\rm N}$ follows a squared Brillouin function for $S$=7/2. By adopting a wavelength-dependent absorption collection, the magnetic structure of EuGa$_4$ was revealed that a nearly full magnetic moment of 6.4$~{\mu}_{\rm B}$ of Eu lies within the basal plane of the lattice. The present study reveals a well-localized divalent Eu magnetism in EuGa$_4$ and demonstrates a high ability of SENJU to investigate materials with high neutron absorption., Comment: 5 pages, 5 figures, 2 Tables. submitted to J. Phys. Soc. Jpn

The structure of inorganic–organic perovskite morpholinium tribromoplumbate C 4 H 8 ONH 2 PbBr 3 has been studied using single-crystal neutron diffraction with the time-of-flight (TOF) Laue technique. Nuclear positions and anisotropic atomic displacement parameters (ADPs) of all the atoms are determined with high accuracy without any restraints. The accuracy of bond lengths and angles in the organic part was almost one digit higher than that of X-ray data, showing the advantage of the neutron Laue technique for the structural study of the present system. It is indicated that the bond lengths and ADPs in the organic part are affected by protonation and bondings between organic and inorganic parts while the conformation of the morpholine molecule in the crystal is retained. The blue-shift in the band gap owing to the distortion in the inorganic octahedra is found in the optical diffuse reflection spectrum and in the electron density of state calculated by ab initio band calculation.

A single-crystal X-ray structure analysis of Co x TiS 2 ( x = 0.26, 0.43, and 0.57) at room temperature has been performed to investigate both the ordered atomic arrangements of intercalated Co atoms and their site occupancies, as well as the nature of the chemical bond from the electron density distribution (EDD) obtained by the maximum entropy method. The superstructures of the Co atoms are observed to be 2 a ×2 a ×2 c unit cells for x = 0.26 and 0.57, and \(\sqrt{3}a{\times}\sqrt{3}a{\times}2c\) unit cells for x = 0.43. The overlapping of EDDs between Co and S atoms and Ti and S atoms corresponds to the covalent bonding in the van der Waals gap layer and TiS 2 layer. It is found that the nature of the covalent bonding between Co and S atoms causes a decrease in the interatomic distance. From in situ X-ray diffraction intensity measurements, the superstructures disappear at 510, 610, and 550 K for x = 0.26, 0.43, and 0.57, respectively. The type of transition for the three specimens is second-order-like.

The structure of α,α-trehalose dihydrate was studied by neutron and X-ray diffraction experiments to understand the relation between its superior biological protective function and the role of the hydrogen bond connecting the trehalose molecules. By direct observation of hydrogen using the neutron diffraction method, the nuclear positions and anisotropic thermal parameters of hydrogen atoms are determined accurately. The nuclear positions show clear discrepancies from the centers of the electron cloud of hydrogen determined from the X-ray data. The result is interpreted in terms of a local electric dipole moment in the hydrogen atoms. The magnitude of the dipole moment is markedly large for the hydrogen atoms participating in the hydrogen bond. The detailed electron density distribution has been determined by using X-ray data obtained at 150 K. It clearly shows the electron cloud of hydrogen spreading over the chain of hydrogen bonds. It was found that there is a part where the electron density is very lo...

A structural study of layered compounds Ni x TiS 2 ( x = 0.30, 0.37, and 0.63) by X-ray and electron diffraction analyses was performed to investigate both the ordered atomic arrangement and disordering behavior of intercalated Ni atoms, and the nature of the chemical bond from the electron density distribution obtained by the maximum entropy method. The 2 a ×2 a ×2 c and \(\sqrt{3}a{\times}\sqrt{3}a{\times}2c\) superstructures of the Ni atoms are observed for x = 0.30 and 0.37 at room temperature, and they disappear at 420 and 425 K with second-order-like behavior. A partial 2 a ×2 a ×2 c ordered arrangement of the Ni atoms is observed at room temperature and disappears at approximately 650 K for x = 0.63. The electron density distribution reveals that the bonding between Ni and S atoms in the van der Waals gap layer has a covalent nature. Such characteristic behavior decreases the interlayer lattice spacing after intercalating Ni atoms into TiS 2 .

An X-ray structural study of single crystals of Mn x TiS 2 ( x =0.13, 0.18, and 0.26) was performed to investigate both the nature of the chemical bond from the electron density distribution (EDD) obtained by the maximum entropy method and local atomic arrangements of intercalated Mn atoms. Mn atoms were intercalated into octahedral sites in the van der Waals gap layer, and interlayer spacing and the distance between each layer were increased by increasing the number of Mn atoms without any change in layered structure. The EDD revealed that covalent bonding exists between Ti and S atoms, and no covalent electrons were found between Mn and S atoms. It is further realized by X-ray diffuse scattering measurements that intercalated Mn atoms are correlated with each other three-dimensionally. In Mn 0.13 TiS 2 and Mn 0.18 TiS 2 , an in-plane ordered structure for the low-temperature phase is expected to be of the 2×2-type in a Wood notation. On the other hand, a \(\sqrt{3}\times\sqrt{3}R30\)°-type ordered struc...