Structural instability and superconductivity in the solid solution SrNi₂(P_1−xGe_x)₂

Abstract

The solid solution SrNi2(P1−xGex)2 with ThCr2Si2‐type structure has been synthesized over the whole composition range by high‐temperature solid state reactions. Structure investigations were performed using X‐ray diffraction (XRD) methods. In addition, in situ temperature‐dependent powder XRD measurements down to 10 K were carried out for two SrNi2(P1−xGex)2 samples with x = 0.110(3) and 0.212(3), which indicate a temperature‐induced collapse of the structure of the first compound around 200 K. For both samples, superconductivity was detected above 1.8 K by magnetic, resistivity, and heat capacity measurements (TC ∼ 3.0 and 2.4 K, respectively). The crystal chemistry and the chemical bonding in the superconducting compounds are discussed in terms of linear muffin‐tin orbital (LMTO) band structure calculations including density of states (DOS), crystal orbital Hamilton populations (COHPs), and a topological analysis using the electron localization function (ELF).

First-Order Phase Transition in BaNi2Ge2 and the Influence of the Valence Electron Count on Distortion of the ThCr2Si2 Structure Type

“…The nickel-based pnictides SrNi 2 P 2 , SrNi 2 As 2 , BaNi 2 P 2 , and BaNi 2 As 2 have recently been found to be superconducting ( T c = 1.4, 0.62, 2.5–3, , and 0.7 K, respectively), along with the chalcogenides KNi 2 S 2 and KNi 2 Se 2 ( T c = 0.5 and 0.8 K, respectively) and the germanide SrNi 2 Ge 2 ( T c = 0.87 K) . Partial substitution at the p-block element or transition-metal site causes an increase of the critical temperature. , For example, the solid solutions BaNi 2 P 2– x Ge x and SrNi 2 P 2– x Ge x show an increase of T c up to 2.9 and 3.0 K, respectively, upon substitution of P atoms by Ge atoms, which can be regarded as a direct hole doping of the superconducting [Ni 2 P 2 ] layers. , …”

Copper Doping of BaNi$_{2}$As$_{2}$: Giant Phonon Softening and Superconductivity Enhancement

“…Nickel-based 122-type compounds, such as BaNi 2 As 2 [1][2][3][4][5][6][7][8], SrNi 2 As 2 [9], BaNi 2 P 2 [10,11], SrNi 2 P 2 [12][13][14][15][16], BaNi 2 Ge 2 [17,18], and SrNi 2 Ge 2 [19] are nonmagnetic analogs of iron-based superconductors. Some of these compounds have provided opportunities for investigating the interplay between structural instability and superconductivity upon chemical doping [7,15,16,18].…”

Qualitative model of high-$T_c$ superconductivity

“…3 in [16] for Fe 1.01 Se. Structural instability and superconductivity in SrNi 2 (P 1x Ge x ) 2 solid solutions was studied in [28]. Magnetic and structural transitions of SrFe 2 As 2 at high P were investigated in [27].…”