12007-07-7Relevant articles and documents
Evidence of multiband behavior in a new superconductor Ta0.8Zr0.2B with FeB-prototype structure
Correa,Nova,de Faria,Santos,de Lima,Nunes,Coelho,Rogl,Fisk,Machado
, p. 597 - 600 (2019)
We present results that show a relation between crystalline structure and superconductivity in the Ta1-xZrxB system. The substitution of Ta for Zr atoms induces a crystal structure change from CrB- to FeB-prototype structure in which superconductivity is present with higher superconducting critical temperature Tc. The interrelation between Tc and Zr content shows a dome-like behavior with maximum Tc at x = 0.2. In this sample, bulk superconductivity was observed and characterized by magnetization, electrical resistivity and specific heat measurements, all consistent with a superconducting critical temperature close to 7.8 K. The upper and lower critical field diagrams have no usual behavior which may be connected to a multiband scenario.
THERMAL EXPANSION STUDIES ON THE GROUP IV-VII TRANSITION METAL DIBORIDES.
Loennberg
, p. 145 - 156 (1988)
The thermal expansions of the group IV-VII transition metal diborides were studied with the aid of X-ray powder diffraction. The diborides were studied over the temperature range 298 - 1500 K. All the diborides except for CrB//2 display larger thermal expansion coefficients in the c direction than in the a direction. The expansion coefficients in the c direction decrease with increasing radius of the metal atom, a fact which can be correlated to an increase in metal-boron bond strength. The thermal expansion coefficient in the a direction changes very little with the size of the metal radius, owing to the fact that the bonding strength in the basal plane is determined by the strong B-B bonds within the boron layer.
Ternary borides Nb7Fe3B8 and Ta7Fe3B8 with Kagome-type iron framework
Zheng, Qiang,Gumeniuk, Roman,Borrmann, Horst,Schnelle, Walter,Tsirlin, Alexander A.,Rosner, Helge,Burkhardt, Ulrich,Reissner, Michael,Grin, Yuri,Leithe-Jasper, Andreas
, p. 9590 - 9600 (2016/07/06)
Two new ternary borides TM7Fe3B8 (TM = Nb, Ta) were synthesized by high-temperature thermal treatment of samples obtained by arc-melting. This new type of structure with space group P6/mmm, comprises TM slabs containing isolated planar hexagonal [B6] rings and iron centered TM columns in a Kagome type of arrangement. Chemical bonding analysis in Nb7Fe3B8 by means of the electron localizability approach reveals two-center interactions forming the Kagome net of Fe and embedded B, while weaker multicenter bonding present between this net and Nb atoms. Magnetic susceptibility measurements reveal antiferromagnetic order below TN = 240 K for Nb7Fe3B8 and TN = 265 K for Ta7Fe3B8. Small remnant magnetization below 0.01μB per f.u. is observed in the antiferromagnetic state. The bulk nature of the magnetic transistions was confirmed by the hyperfine splitting of the M?ssbauer spectra, the sizable anomalies in the specific heat capacity, and the kinks in the resistivity curves. The high-field paramagnetic susceptibilities fitted by the Curie-Weiss law show effective paramagnetic moments μeff ≈ 3.1μB/Fe in both compounds. The temperature dependence of the electrical resistivity also reveals metallic character of both compounds. Density functional calculations corroborate the metallic behaviour of both compounds and demonstrate the formation of a sizable local magnetic moment on the Fe-sites. They indicate the presence of both antiferro- and ferrromagnetic interactions.
REACTION BETWEEN REFRACTORY METALS AND INSULATING NITRIDES AT HIGH TEMPERATURE
SATA T,URANO T
, p. 21 - 29 (2008/10/08)
Some nitrides, BN, AIN and Si//3N//4, are used as electric insulators up to moderate temperatures. The difficult problems occur when they are to be employed at higher temperatures than 2000 C. In this paper the reactions between these insulators and conductors of refractory metals, tungsten and tantalum, are investigated up to 2100 C in a tungsten furnace under argon atmosphere.
