Sc₃Co, a new structure type related to Fe₃C and Re₃B by periodic unit-cell twinning

Abstract

Sc3Co, orthorhombic, Pnma, a = 13.102 (9), b = 8.624 (6), e = 5.829 (3) A, Z = 8, D x = 3.913 g cm -3, g(Mo Ka) = 107 cm -1. Least-squares refinement gave R = 0.048 for 535 independent diffractometer data which were corrected for absorption. The structure is characterized by trigonal prisms of Sc atoms which are centred by Co atoms. Centred trigonal prisms are also found in the Fe3C and Re3B structure types. Using the concept of periodic unit-cell twinning, the point positions of all three structure types can be derived. Fe3C is based on a hexagonal, and Re3B on a cubic close-packed base structure, while Sc3Co derives from a closepacked base structure with mixed stackings corresponding to the atom arrangement in the Nd structure type. IntroductionThe compound ScaCo was prepared by the arc-melting technique from elements of high purity (Sc 99.95%, Co 99.99%). A single trigonal prismatic crystal (base: 0.14 x 0.12 x 0.12 mm, height: 0.14 mm) was isolated from the crushed melt. Systematic absences in precession photographs showed the space group to be either Pn21a or Pnma (Okl with k + l = 2n + 1 and hk0 with h --2n + 1). Intensities of 588 independent reflexions out to a limit of sin 0/2 = 0.702 A -1 were measured with graphite-monochromated Mo K, 3174 Sc3Co, A NEW STRUCTURE TYPE RELATED TO Fe3C AND Re3B radiation on a Philips PW 1100 automatic four-circle diffractometer in the 0--20 scan mode. Cell parameters were determined from least-squares refinement of the 20 values of 30 reflexions using the program PARAM (XRAY system, 1976). An empirical absorption correction, based on the comparison of several sets of equivalent reflexions, was applied with the program CAMEL JOCKEY (Flack, 1977). The structure was solved by direct methods in the space group Pnma. The phases of the 230 reflexions with IEI > 1.2 were determined with SINGEN and TANGEN (XRAY system, 1976). Positional and isotropic thermal parameters refined satisfactorily with the least-squares program CR YLSQ (XRAY system, 1976 Zr3Co (Kripyakevich, Marvik & Burnasova, 1970), Y3Rh2 (Moreau, Paccard & Parth6, 1975), YsCo5 (Moreau, Paccard & Parth+, 1976) and Y3Ni2 (Le Roy, Moreau, Paccard & Parth~, 1977). DiscussionInformation on the Sc-rich part of the Sc--Co phase diagram is limited. The existence of the following phases has been reported: ScCo with CsCI structure type (Aldred, 1962), Sc2Co with CuAI 2 type (Aldred, 1962) and Sc3Co supposedly isostructural with ZraCo (Markiv, Pet'kov, Gavrilenko & Beryavina, 1974 4Re (1) BERNARD CHABOT AND ERWIN PARTHl3 3175intensities and line positions it was obvious that Re3B and Sc3Co were not of the same type. The present study demonstrates that Sc3Co crystallizes with a new structure type. A drawing of the Sc3Co structure is presented in Fig. 1. The structure is characterized by trigonal prisms of Sc atoms which are centred by Co atoms. From the interatomic distances (Table 2) :O aFe3c = ~ a n = 1.915a. Table 1. Except for the z values, the point positions of Re3B (Table 1) cannot be read directly from the dr...

The μ3Model of Acids and Bases: Extending the Lewis Theory to Intermetallics

“…In Figure , we show the results of applying this μ 3 acidity analysis to DFT-calibrated Hückel models for other members of this family. μ 3 -Neutralization bar graphs are plotted for 17 phases chosen to span a wide range of electronegativity differences, as well as some of the structural diversity in this family. ,− …”

Development of a nanostructured Zr3Co intermetallic getter powder with enhanced pumping characteristics

“…(4) It was found that longer heat treatment time and higher heat treatment temperature facilitate the formation of Zr 3 Co phase. (5) The results showed that after mechanical alloying time of 16 h and optimum heat treatment (at 330 C for 60 min), nanostructured Zr 3 Co intermetallic powder was achieved. (6) The synthesized Zr 3 Co intermetallic powders showed an enhanced pumping properties and improved capacity for hydrogen sorption in contrast to the similar commercial getter.…”

Changes in electronic, magnetic and bonding properties from Zr2FeH5 to Zr3FeH7 addressed from ab initio

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