Specific heat and magnetization of the superconducting monoxides: NbO and TiO

Okaz, Ali M.; Keesom, P. H.

doi:10.1103/physrevb.12.4917

Cited by 43 publications

(10 citation statements)

References 29 publications

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“…41 The homogeneity range for NbO, determined from the samples quenched from the melting point to room temperature is 0.98 e O/Nb e 1.02. 42 According to the phase diagram for the Nb-O system proposed by Naito et al, 17 the homogeneity ranges for NbO 2 and Nb 12 O 29 at T ) 1223 K are 1.9995 e O/Nb e 2.0023 and 2.4230 e O/Nb e 2.4330, respectively. The homogeneity range of the nonstoichiometric Nb 2 O 5-x phase has been determined by X-ray diffractrometry, 43,44 chemical analysis, 44 thermogravimetry, 16,45,46 electrical conductivity, 16 and electrochemical measurement.…”

Section: Introductionmentioning

confidence: 99%

“…The homogeneity range for NbO, determined from the samples quenched from the melting point to room temperature is 0.98 ≤ O/Nb ≤ 1.02 . According to the phase diagram for the Nb−O system proposed by Naito et al, the homogeneity ranges for NbO 2 and Nb 12 O 29 at T = 1223 K are 1.9995 ≤ O/Nb ≤ 2.0023 and 2.4230 ≤ O/Nb ≤ 2.4330, respectively.…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamic Properties of Niobium Oxides

et al. 2010

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Thermodynamic properties of three oxides of niobium have been measured using solid state electrochemical cells incorporating yttria-doped thoria (YDT) as the electrolyte in the temperature range T = (1000 to 1300) K. The standard Gibbs energies of formation of NbO, NbO2, and NbO2.422 from the elements can be expressed as: △ f G NbO o ± 547 / J · mol − 1 = − 414 986 + 86 .861 ( T / normalK ) △ f G NbO 2 o ± 548 / J · mol − 1 = − 779 864 + 164 .438 ( T / normalK ) △ f G NbO 2.422 o ± 775 / J · mol − 1 = − 911 045 + 197 .932 ( T / normalK ) The results are discussed in comparison with thermodynamic data reported in the literature. The new results refine data for NbO and NbO2 presented in standard data compilations. There are no data in thermodynamic compilations for NbO2.422 (Nb12O29). In the absence of the heat capacity and enthalpy of formation measurements, only the Gibbs energy of formation of NbO2.422 can be assessed. The free energy of formation of stoichiometric Nb2O5 is evaluated on the basis of measurements on NbO2.422 and information available in the literature on phase boundary compositions and isothermal variation of nonstoichiometric parameter with oxygen potential for Nb2O5−x . The results suggest a minor revision of data for Nb2O5. A minimum in the Gibbs energy of mixing for the system Nb−O occurs in the nonstoichiometric domain of Nb2O5−x with x = 0.036.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermodynamic Properties of Niobium Oxides

et al. 2010

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“…All spectra are normalized to their integrated intensities after the subtraction of the standard integral background to account for inelastic scattering processes [27]. All the spectra show a clear cutoff at zero energy (E F , Fermi level), consistent with the system being a good metal [17,[28][29][30]. All spectra are comparable to one another in terms of the total band width and peak positions, affirming their intrinsic nature.…”

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confidence: 69%

“…Density functional based band structure calculations have been performed [12,[14][15][16] to explain the properties of niobium monoxide [17][18][19][20] and it was found that the Nb 3 O 3 structure is more stable than the Nb 4 O 4 by about 1 eV per NbO unit [15,16]. Our objective here is to test experimentally the accuracy of band structure calculations and to identify the bands in the measured spectra that are characteristic for Nb 3 O 3 , thereby proving that the vacancies are ordered and that band formation is an essential ingredient for the formation of vacancies in niobium monoxide.…”

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confidence: 99%

Electronic signature of the vacancy ordering in NbO(Nb3O3)

et al. 2017

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We investigated the electronic structure of the vacancy-ordered 4d-transition metal monoxide NbO (Nb3O3) using angle-integrated soft-and hard-x-ray photoelectron spectroscopy as well as ultra-violet angle-resolved photoelectron spectroscopy. We found that density-functional-based band structure calculations can describe the spectral features accurately provided that self-interaction effects are taken into account. In the angle-resolved spectra we were able to identify the so-called vacancy band that characterizes the ordering of the vacancies. This together with the band structure results indicates the important role of the very large inter-Nb-4d hybridization for the formation of the ordered vacancies and the high thermal stability of the ordered structure of niobium monoxide.

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“…4,5 The NbO 2 with d 1 Nb 4+ undergoes an insulator-to-metal transition at approximately 1000 K, which is accompanied by a structural transition from a distorted rutile phase (low-temperature phase) to a rutile phase (high-temperature phase). 6,7 The NbO with d 3 Nb 2+ behaves as a superconductor below a critical temperature of 1.4 K. 8,9 Numerous unique and useful properties have been reported for mixed-cation oxides containing Nb. 1,10 For example, LiNbO 3 is a uniaxial ferroelectric material with rhombohedral symmetry, whose polarization is along the threefold z-axis.…”

Section: Introductionmentioning

confidence: 99%