Crystal structure of cobalt chromium germanium, CoCrGe

Abstract

CoCrGe, hexagonal, P^mmc (No. 194), a = 4.092(1) Ä, c = 5.145(2) Ä, V= 74.6 Ä 3 , Z= 2, R e (F) = 0.049, wR m (F 2 ) = 0.097, Γ= 300 K. Source of materialSingle crystals of cobalt chromium germanium were grown by chemical vapour transport in a closed quartz ampoule. Iodine was used as transporting agent. The metals and the transporting agent were heated at 1148 Κ for seven days to homogenize the source material. The chemical vapour transport was performed at 1073 Κ -> 1223 Κ. After seven days, the deposition of single crystals with different compositions can be observed in the crystallisation zone. Within these products crystals of the composition CoCrGe (EDX-analysis) were found and isolated. The figure shows an euhedral crystal of about 0.5 mm diameter.For the data collection a smaller crystal without well developed faces was used.The empirical absorption correction was based on a function of the mean intensity of the imaging plate versus angle phi using program DECAY of the Stoe IPDS software package.A spherical absorption correction with μίΙ = 1.8 was applied too using program SPHERE of the PROMETHEUS sy stem [ 1 ]. The absorption correction improved the iiint from 0.187 to 0.142. DiscussionThe structure of CoCrGe can be derived from the Ni2ln type. From our X-ray analysis we conclude that position 2a is occupied by Cr, 2c by Co and 2d by Ge. Co and Ge may be interchanged. The high temperature phase of CoGeMn, e.g., is known to have this structure [2], According to the TYPIX database [3] the structure belongs to the BeZrSi-type, but BeZrSi has a much higher da ratio. Related phases in the binary system Co-Ge are Coi.7sGe (called "Co2Ge" [4]) and CosGe3, but in these phases at least one occupation factor for Co is <1. Therefore these phases have a smaller cell volume. The lattice constants of "Co2Ge" are reported as a = 3.940 Ä and c = 5.018 A. The higher displacement factor of Co and the lower one of Cr suggest that there might be a mixed occupation of positions 2a and 2c, for instance (0.9 Cr + 0.1 Co) on la and (0.9 Co + 0.1 Cr) on 2c. But trials to refine this model yield only very small amounts of the minor element in both positions with large errors and no significant reduction of the, where an explanation is given for the large value of Bco). If one refines anisotropic displacement parameters thermal ellipsoids are obtained which are comparable to those in CoGeMn (HT), namely elongated ellipsoids for Co and Ge and a flattened ellipsoid for the 2a metal with respect to the hexagonal c axis. For this comparison the parameters of CoGeMn (HT) given in [2] have to be transformed by an origin shift of 01/41/4 followed by a multiplication with matrix 002/011 /-100, because in [2] the structure is described in terms of an orthorhombic cell which simplifies the comparison to the low temperature phase of CoGeMn. The refinement of anisotropic displacement parameters improves the R values considerably, but because of the small number of observed reflections in the unique data set the isotropic structure m...

Effects of Ge addition on the structure, mechanical and magnetic properties of (CoCrFeNi)100-xGex high-entropy alloys

“…All the diffraction peaks can be indexed with a hexagonal structure, and the lattice parameters of a and c are 4.092 (1) Å and 5.145 (2) Å, respectively. Further analysis found that this new phase is isostructural to the hexagonal structure of CrCoGe reported before [23], which has a space group of P6 3 /mmc.…”

First-principles investigation of half-metallic ferromagnetism of half-Heusler compounds XYZ

“…. For CoCrGe, CoFeGe, FeMnGe, FeMnP and FeCrAs, the ground state is hexagonal Ni 2 In structure [27][28][29][30]. Their metastable energies for the half-Heusler structure are 0.14, 0.18, 0.22, -0.02 and -0.54 eV, respectively.…”

“…Nine half-Heusler half-metals are predicted with the half-metallic gap of 0.07-0.67 eV. In fact, most of these nine compounds crystallize in hexagonal Ni 2 In structure in the bulk form [27][28][29][30], and some of them exhibited the property of phase transformation, forming orthorhombic TiNiSi structure [31][32][33][34][35]. In order to investigate the possibility of experimentally fabrication of these half-Heusler half metals, we further reveal from the structural stability that the formation energies for these nine half-Heusler compounds are negative, thus suggesting a possibility of synthesizing these half-metals in the experiment.…”

Half-metallicity versus Symmetry in Pt, Ni and Co-based Half Heusler Alloys: A First-principles Calculation

“…9 On the contrary, it has been seen in the literature that many of the half Heusler alloy samples exhibit non-cubic symmetries but there is no explicit discussion on the half-metallicity in these materials. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] It has been observed that NiMnSb and some other ABSb, as well as ABSn materials possess cubic C1 b symmetry. 24 On the other hand, while NiMnGe is seen to exhibit an orthorhombic P nma space-group at room temperature, 25 NiMnGa has a hexagonal symmetric structure.…”

“…20 Further, ABSi or ABGe or ABP or ABAs compounds are seen to exhibit either an orthorhombic structure (with P nma space-group) or a hexagonal phase (with either P 6 3 /mmc or P 62m space-group). [10][11][12][13][14][15][16][17][18][19][20][21][22][23] In the literature, there are also reports that, many samples of HHAs are seen to exhibit more than one symmetries. For example, each of NiMnAs and NiMnP are reported to possess both orthorhombic and hexagonal structures.…”