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27 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Tb(CoGe)2 by Materials Project

TbCo2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Tb is bonded in a 8-coordinate geometry to eight equivalent Co and eight equivalent Ge atoms. All Tb–Co bond lengths are 3.22 Å. All Tb–Ge bond lengths are 3.09 Å. Co is bonded to four equivalent Tb and four equivalent Ge atoms to form a mixture of distorted edge, face, and corner-sharing CoTb4Ge4 tetrahedra. All Co–Ge bond lengths are 2.34 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Tb, four equivalent Co, and one Ge atom. The Ge–Ge bond length is 2.60 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sm(CoGe)2 by Materials Project

SmCo2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sm is bonded in a 8-coordinate geometry to eight equivalent Co and eight equivalent Ge atoms. All Sm–Co bond lengths are 3.25 Å. All Sm–Ge bond lengths are 3.13 Å. Co is bonded to four equivalent Sm and four equivalent Ge atoms to form a mixture of distorted corner, edge, and face-sharing CoSm4Ge4 tetrahedra. All Co–Ge bond lengths are 2.35 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Sm, four equivalent Co, and one Ge atom. The Ge–Ge bond length is 2.67 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(CoGe)2 by Materials Project

HoCo2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho is bonded in a 8-coordinate geometry to eight equivalent Co and eight equivalent Ge atoms. All Ho–Co bond lengths are 3.21 Å. All Ho–Ge bond lengths are 3.08 Å. Co is bonded to four equivalent Ho and four equivalent Ge atoms to form a mixture of distorted corner, edge, and face-sharing CoHo4Ge4 tetrahedra. All Co–Ge bond lengths are 2.33 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Ho, four equivalent Co, and one Ge atom. The Ge–Ge bond length is 2.57 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nd(CoGe)2 by Materials Project

NdCo2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Nd is bonded in a 8-coordinate geometry to eight equivalent Co and eight equivalent Ge atoms. All Nd–Co bond lengths are 3.27 Å. All Nd–Ge bond lengths are 3.15 Å. Co is bonded to four equivalent Nd and four equivalent Ge atoms to form a mixture of distorted corner, edge, and face-sharing CoNd4Ge4 tetrahedra. All Co–Ge bond lengths are 2.35 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Nd, four equivalent Co, and one Ge atom. The Ge–Ge bond length is 2.72 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Gd(CoGe)2 by Materials Project

GdCo2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd is bonded in a 8-coordinate geometry to eight equivalent Co and eight equivalent Ge atoms. All Gd–Co bond lengths are 3.23 Å. All Gd–Ge bond lengths are 3.11 Å. Co is bonded to four equivalent Gd and four equivalent Ge atoms to form a mixture of distorted edge, face, and corner-sharing CoGd4Ge4 tetrahedra. All Co–Ge bond lengths are 2.34 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Gd, four equivalent Co, and one Ge atom. The Ge–Ge bond length is 2.63 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Er(CoGe)2 by Materials Project

ErCo2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Er is bonded in a 8-coordinate geometry to eight equivalent Co and eight equivalent Ge atoms. All Er–Co bond lengths are 3.20 Å. All Er–Ge bond lengths are 3.07 Å. Co is bonded to four equivalent Er and four equivalent Ge atoms to form a mixture of distorted edge, corner, and face-sharing CoEr4Ge4 tetrahedra. All Co–Ge bond lengths are 2.33 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Er, four equivalent Co, and one Ge atom. The Ge–Ge bond length is 2.56 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tm(CoGe)2 by Materials Project

TmCo2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Tm is bonded in a 8-coordinate geometry to eight equivalent Co and eight equivalent Ge atoms. All Tm–Co bond lengths are 3.20 Å. All Tm–Ge bond lengths are 3.06 Å. Co is bonded to four equivalent Tm and four equivalent Ge atoms to form a mixture of distorted face, edge, and corner-sharing CoTm4Ge4 tetrahedra. All Co–Ge bond lengths are 2.33 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Tm, four equivalent Co, and one Ge atom. The Ge–Ge bond length is 2.55 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Centrosymmetric or Noncentrosymmetric? Transition Metals Talking in K 2 TGe 3 S 8 (T = Co, Fe)

Two new quaternary sulfides K 2 TGe 3 S 8 (T=Co, Fe) have been synthesized by a high-temperature solid-state routine and flux growth method. The crystal growth process of K 2 TGe 3 S 8 (T=Co, Fe) was elucidated by in-situ powder X-ray diffraction and DSC thermal analysis. The mm-sized crystals of K 2 TGe 3 S 8 (T=Co, Fe) were grown. K 2 CoGe 3 S 8 crystallizes in a new structure type in centrosymmetric space group P1¯ (No. 2) with unit cell parameters of a = 7.016(1) Å, b = 7.770(1)Å, c = 14.342(1) Å, α = 93.80(1)°, β = 92.65(1)°, γ = 114.04(1)°. K 2 FeGe 3 S 8 crystallizes in K 2 FeGe 3 Se 8 structure type and the noncentrosymmetric space group P2 1 (No. 4) with unit cell parameters of a = 7.1089(5)Å, b = 11.8823(8)Å, c = 16.7588(11)Å, β = 96.604(2)°. There is a high structural similarity between K 2 CoGe 3 S 8 and K 2 FeGe 3 S 8 . The larger volume coupled with higher degrees of distortion of [FeS 4 ] tetrahedra compared to [CoS 4 ] tetrahedra accounts for the structure’s shift from centrosymmetric to noncentrosymmetric. The theory simulation confirms that [TS 4 ]T= Co or Fe tetrahedra play a crucial role in controlling the structure and properties of K 2 TGe 3 S 8 (T = Co, Fe). The measured optical bandgaps of K 2 CoGe 3 S 8 and K 2 FeGe 3 S 8 are 2.1(1) eV and 2.6(1) eV respectively. K 2 FeGe 3 S 8 shows antiferromagnetic ordering at 24K while no magnetic ordering was detected in K 2 CoGe 3 S 8 . In conclusion, the magnetic measurements also demonstrate the divalent nature of transition metals in K 2 TGe 3 S 8 (T = Co, Fe).

36 MATERIALS SCIENCE↗
DOE OSTI2020

The influence of Au substitution and hydrostatic pressure on the phase transitions and magnetocaloric properties of MnCoGe alloys

In this work, the phase transitions and magnetocaloric properties of Mn 1--x Au x CoGe (0≤x≤0.025) alloys were studied as a function of concentration x and applied hydrostatic pressure. The increasing substitution of Au for Mn results in the decrease of the first-order martensitic transition temperature, and this first-order martensitic transition was ultimately converted to a second-order magnetic transition when the Au substitution (x) reached 0.025. The magnitudes of the maximum magnetic entropy changes increased when the magnetic and structural transitions were coupled, which occurred for 0.005≤x≤0.020. The largest maximum magnetic entropy change for a field change of μ 0 ΔH=7 T was 33.1J/kgK for the sample with x=0.020. Similar to the effect of Au substitution, the first-order martensitic transition temperature initially decreased, and then converted to second order, when the applied hydrostatic pressure reached a large enough value. Interestingly, both Au substitution and pressure application cause a volume reduction and, in both cases, the first-order martensitic transition temperature initially reduced and then converted to second-order. These results suggest two different methods of tuning the transition temperatures in these magnetocaloric materials. One can either apply hydrostatic pressure and temporarily adjust the transition temperatures or modify the composition chemically and permanently change the transition temperatures.

36 MATERIALS SCIENCE↗