Noriaki Okubo

Nuclear Quadrupole Coupling Constants in Niobium Pentachloride and Related Compounds (I) Halogen Nuclei

35 Cl NQR spectrum in NbCl 5 has been investigated from 4.2 K to 480 K. The lines of about 7 MHz have larger multiplicity and show positive temperature dependence incontrast to the usual negative one for the line of about 13 MHz. The former lines are further separated into two groups having different temperature dependences. The expressions for the chlorine coupling constant are derived according to Townes-Daileys method on the basis of the p π -d π bond. The NQR data are analysed and the lines are assigned to the axial, equatorial and bridging chlorine atoms in the Nb 2 Cl 10 dimer. The theory is applied to other related compounds.

Anomalies of 93Nb and 35Cl NQR in niobium pentachloride

Abstract The temperature dependence of 93 Nb and 35 Cl NQR in niobium pentachloride has been investigated from 4.2 K to 480 K. An anomalous temperature dependence has been found for the saturation behaviour of 35 Cl lines and for the resonance frequencies of 93 Nb and 35 Cl lines.

Nuclear Quadrupole Coupling Conrtants in Niobium Pentachloride and Related Compounds (II) Transition Metal Nuclei

93 Nb NQR spectrum in NbCl 5 has been investigated from 4.2 K to 480 K. The coupling constant shows an unusual positive temperature dependence at low temperatures. The EFG tensor is calculated with the d 2 sp 3 octahedral bond functions. The experimental data are analysed in terms of the contributions from the σ- and π-bonds. It is shown that the positive temperature dependence can be explained by the p π -d π bond mechanism. The theory is also applied to the related compounds and the consistency with the analysis of the halogen coupling constants is shown.

93Nb Nuclear Quadrupole Resonance in Orthorhombic Phase of Niobium Pentabromide

The 93 Nb NQR has been investigated in one phrase of NbBr 5 which was identified to be orthorhombic by the X-ray analysis. The resonance frequencies have been measured between 4.2 K and 423 K, its melting point. The coupling constant showed a positive temperature dependence up to melting point. The temperature dependence of the coupling constant is compared between NbBr 5 and NbCl 5 from the view point of π-bond character.

35Cl Nuclear Quadrupole Resonance in Tantalum Pentachloride

35 Cl NQR spectrum and its temperature dependence in tantalum pentachloride are reported and compared with those in the related compounds. The temperature dependence is discussed in detail in relation with π-bond character.

81Br Nuclear Quadrupole Relaxation in Aluminium Tribromide

Abstract The 81Br nuclear spin-lattice relaxation time in AlBr3 has been measured between 8 K and room temperature. The result is analyzed using the theory of the Raman process based on covalency. A Debye temperature of 67.6 K and covalency of 0.070 and 0.072 for terminal and 0.022 for bridging bonds are obtained. The correspondence of the latter values to those obtained from the NQR frequencies is low, in contrast to the previously examined compounds.

35Cl Nuclear Quadrupole Relaxation in Antimony Trichloride

Abstract The 35Cl NQR frequency and spin-lattice relaxation time in SbCl3 have been measured between 10 K and the melting point. The relaxation at low temperatures is attributed to the Raman process. A Debye temperature of 141 K and covalencies 0.390 and 0.356 are obtained. The latter values correspond well to those obtained from the NQR frequencies. For the relaxation above 200 K two more mechanisms are considered.

79Br Nuclear Quadrupole Relaxation in the High Temperature Modification of Niobium Pentabromide

Abstract The spin-lattice relaxation time of 79Br NQR has been measured between 4.2 K and room temperature. The result is compared with that of 35Cl NQR in NbCl5. The origin of the relaxation is attributed to the quadrupolar interaction and the temperature dependence is explained by the Raman process. The Debye temperature is determined to be 94 K and the relaxation time is related with the NQR frequency through the covalency.

93Nb Nuclear Spin-Spin Relaxation in the Low-Dimensional Antiferromagnet Fe0.25NbS2

93Nb nuclear spin-spin relaxation has been examined in the low-dimensional antiferromagnet Fe0.25NbS2 between 4.2 K and 300 K. The relaxation is characterized by two T2’s. The temperature dependence is discussed together with the origin of the disappearance of the fast decay at low temperatures.

Positive Temperature Dependence of Quadrupole Splittings in Mössbauer Spectra of Fe1.33Nb2.67Se10

The Mössbauer effect in the low-dimensional compound Fe1.33Nb2.67Se10 has been examined between 78 and 414 K. An anusual positive temperature dependence of the quadrupole splittings was found above 250 K. As a possible origin a mechanism due to π bonding is suggested