Masakazu Kunitomo

Characterization of hydrated sodium molybdenum bronzes

Abstract Two kinds of hydrated sodium molybdenum bronzes, an air-dried bronze (AD) and a vacuum dried one (VD), are characterized using X-ray diffraction, TG-DTA, IR spectroscopy, and NMR. According to NMR results, the paired protons and a small amount of isolated protons fixed in position are included both in AD and VD. It is found that the hydrate-water (HW) in VD exists basically in the form of hydrated sodium ion, Na+(H2O)2, where Na+ coordinates with four terminal oxygens of an (MoO6) octahedron of MoO3 and two oxygens of hydrate-water (HW-2). The composition of VD has been determined as [Na(H2O)1.95]0.22H0.03MoO3.11. In addition to HW-2, AD includes another hydrate-water (HW-1), which is easily removed by drying in vacuo and/or by standing in air. The composition of AD has been determined as [Na(H2O)2+2.26]0.23H0.02MoO3.10.

Rotating-Frame Nuclear-Double-Resonance in NaCl: Spin-Calorimetry and Multiple-Spin-Flips

An experiment of the nuclear double resonance in the rotating frame is carried out on Na 23 -Cl 35 system in a single crystal of NaCl. The double resonance signals caused by one sodium spin flip accompanied by two chlorine flips, and by one chlorine flip accompanied by two sodium flips are observed, in addition to the ordinary signals caused by one sodium and one chlorine flips. The experimental results are analyzed from the viewpoint of thermodynamics (spin-calorimetry) and an effect of Cl 35 spin-lattice relaxation on the double resonance is taken into account. The spin-lattice relaxation time of Cl 35 is measured by using the double resonance spectrum obtained. In addition, a sensitive technique, available in the NMR experiments in solids, is developed to a resonant value for a given rf frequency.

Protonic location in hydrogen molybdenum bronzes HxMoO3 as studied by proton NMR lineshape analysis

Abstract Rigid lattice proton NMR spectra are observed in four types of hydrogen molybdenum bronzes H x MoO 3 with pulsed NMR. Lineshapes of the spectra are analyzed by computer-simulation. We conclude that the spectrum of type I (0.21 ≦ x ≦ 0.40) is a superposition of the spectrum originating in a two-spin system (Pake-doublet) and the one originating in a three-spin system. On the other hand, the spectra of types II (0.85 ≦ x ≦ 1.04), III (1.55 ≦ x ≦ 1.72), and IV ( x ⋍ 2.0) consist of a Pake-doublet, a Gaussian, and a Lorentzian. The Gaussian and the Lorentzian are attributed to isolated and immobile protons, and mobile protons, respectively. From the analyses, portions of hydrogen contents of different locations and distances between nearest neighbor protons are determined for all four types of the bronzes. Transition of the protonic structure from type I to II is discussed.

Nuclear magnetic resonance and differential thermal analysis studies of hydrogen molybdenum bronzes, HxMoO3

NMR and DTA studies were carried out on four phases of hydrogen molybdenum bronzes, types I–IV. From DTA and X-ray data it is confirmed that the bronze with the highest hydrogen content changes successively to that with lowest hydrogen content and finally to MoO3, by evolution of H2. NMR spectra of types II–IV obtained in the present study can be clearly resolved into three components, a Pake doublet, a Gaussian and a Lorentzian, which are attributed to paired protons, isolated protons fixed on a site, and moving protons, respectively. The phase changes of the bronzes are discussed by connecting them with hydrogen insertion. A preliminary result of computer-simulation analyses of the lineshapes is also given.

NMR in KH_2PO_4 by Double Resonance Method

NMR signals of the potassium in KH 2 PO 4 were detected by means of the double resonance technique in the rotating reference frame, and the electric quadrupole coupling constants and associated parameters were determined in the paraelectric (290°K) and ferroelectric (77°K) phases. At 290°K, the electric field gradient at the site of the potassium is axially symmetric (η=0) and | e Q q / h |=1.68 MHz for K 39 . At 77°K, | e Q q / h |=1.479 MHz for K 39 and 1.796 MHz for K 41 with the asymmetry parameter η=0.696. The major principal axis of the electric field gradient tensor coincided with the Z ( c )-axis in both phases. The values of the electric field gradient were calculated by using point charge model in both paraelectric and ferroelectric phases and compared with the experimental ones.NMR signals of the potassium in KH 2 PO 4 were detected by means of the double resonance technique in the rotating reference frame, and the electric quadrupole coupling constants and associated parameters were determined in the paraelectric (290°K) and ferroelectric (77°K) phases. At 290°K, the electric field gradient at the site of the potassium is axially symmetric (η=0) and | e Q q / h |=1.68 MHz for K 39 . At 77°K, | e Q q / h |=1.479 MHz for K 39 and 1.796 MHz for K 41 with the asymmetry parameter η=0.696. The major principal axis of the electric field gradient tensor coincided with the Z ( c )-axis in both phases. The values of the electric field gradient were calculated by using point charge model in both paraelectric and ferroelectric phases and compared with the experimental ones.

Proton NMR Study of Molecular Crystal Ferroelectrics, Trichloroacetamide (TCAA)

Proton spin lattice relaxation time was measured and proton NMR spectrum was observed in a purely molecular ferroelectrics, trichloroacetamide (TCAA). From the temperature and the frequency depende...

Preparation and characterization of a sodium insertion compound of hydrogen molybdenum bronze, Na0.25(H2O)y[H0.21MoO3]

new red hydrogen–sodium co-insertion compound of molybdenum trioxide, Na0.25(H2O)y[H0.21MoO3], has been prepared which possesses sodium ions in its interlayer space and protons in the intralayer positions. Two phases of this compound were observed depending on hydration water content. According to XRD investigations, there was little difference in crystal structure between this compound and hydrated sodium molybdenum bronze. The Na–H co-insertion molybdenum bronze was characterized by XRD, NMR and thermogravimetric and differential thermal analysis (TG–DTA) and showed an interesting structural transformation atca. 550 K which was related to the change in interlayer spacing. It is suggested that the transformation results from structural defects generated by dehydration due to intralayer protons.

Observation of double Pake doublet in a sodium insertion compound of hydrogen molybdenum bronze

Abstract It was revealed by computer-simulation that a rigid lattice proton NMR spectrum in a new sodium insertion compound of hydrogen molybdenum bronze, [Na(H 2 O) y ] 0.25 H 0.21 MoO 3 , consists of two Pake doublets and a Gaussian. One of the Pake doublets originates in pairs of intralayer protons and the other in a proton in H 2 O.

Proton insertion compound with tunnel structure

Abstract The hexagonal hydrogen insertion compound, hexH x MoO 3 , with the tunnel structure was obtained from sodium decamolybdate, Na-deca. A maximum amount of inserted hydrogen was x =1.5. Hydrogen insertion accompanied the insertion of hydrate water. NMR results prove the presence of the paired protons and the isolated protons fixed in the position. When the protons were inserted, they were distributed into the paired protons and the isolated ones. The model of hydrogen insertion was proposed.

Multiple spin echoes in inhomogeneously broadened NMR systems

Abstract New types of spin echoes produced by refocusing the magnetic moments dephased during a long rf excitation pulse are observed in inhomogeneously broadened NMR systems. The experimental results are in good agreement with the theoretical predictions.