X-ray powder-diffraction patterns for (a) SrNi2Ge2 with stable bct phase (space group ), (b) SrPd2Ge2 with stable bct phase, and (c)SrPt2Ge2 with stable monoclinic phase (space group ). The asterisks indicate the possible positions of metastable bct phase.
Crystal structure of (a) stable monoclinic SrPt2Ge2 (space group ) and (b) metastable bct structure (space group ). Instead of two PtGe4 layers in the bct structure, the monoclinic structure contains one PtGe4 layer and one GePt4 layer with interchanged Pt and Ge atomic positions.
Molar magnetic susceptibility in both 10-G FC and ZFC modes are superimposed of molar heat capacity C(T) for the stable bct SrPd2Ge2 compound with bulk Tc of 3.2 K. 23–25
Molar magnetic susceptibility of SrPt2Ge2 compound under low applied magnetic fields in both FC and ZFC modes. Tc onset at 10.2 K was observed, a much smaller diamagnetic signal indicates that the superconductivity is not from the stable monoclinic phase but from the metastable bct phase as in SrPd2Ge2.
Diamagnetic hysteresis curves at for superconducting SrPt2Ge2.
X-ray powder-diffraction patterns of three Sr(Pd1− x Pt x )2Ge2 compounds (x = 0.1, 0.25, and 0.5). Stable monoclinic phase mixed with minor metastable bct phase was observed with 25% and 50% Pt substitution.
Molar magnetic susceptibility of five Pt-poor compounds Sr( Pt x )2Ge2 (x = 0, 0.1, 0.15, 0.2, and 0.25) in 20-G ZFC mode. Bulk Tc was observed for with the stable bct phase. Metastable Tc was observed for x = 0.2 and 0.25.
Molar magnetic susceptibility of three Pt-rich compounds Sr( Pt x )2Ge2 (x = 0.5, 0.7, and 1.0) in 20-G ZFC modes. Metastable Tc increases from 7.5 K for x = 0.5 to 10.2 K for x = 1.0.
Variation of superconducting transition temperatures Tc (x) for the Sr( Pd x )2Ge2 system 23 and the Sr( Pt x )2Ge2 system ( ). Structural phase transition from bct to monoclinic occurs near .
Atomic positions of stable monoclinic SrPt2Ge2 (space group , No. 4) with lattice parameters a = 0.4401(4) nm, b = 0.4435(4) nm, c = 0.9764(10) nm, and .
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