Na1−xSn2P2 as a new member of van der Waals-type layered tin pnictide superconductors

Abstract

Superconductors with a van der Waals (vdW) structure have attracted a considerable interest because of the possibility for truly two-dimensional (2D) superconducting systems. We recently reported NaSn2As2 as a novel vdW-type superconductor with transition temperature (Tc) of 1.3 K. Herein, we present the crystal structure and superconductivity of new material Na1−xSn2P2 with Tc = 2.0 K. Its crystal structure consists of two layers of a buckled honeycomb network of SnP, bound by the vdW forces and separated by Na ions, as similar to that of NaSn2As2. Amount of Na deficiency (x) was estimated to be 0.074(18) using synchrotron X-ray diffraction. Bulk nature of superconductivity was confirmed by the measurements of electrical resistivity, magnetic susceptibility, and specific heat. First-principles calculation using density functional theory shows that Na1−xSn2P2 and NaSn2As2 have comparable electronic structure, suggesting higher Tc of Na1−xSn2P2 resulted from increased density of states at the Fermi level due to Na deficiency. Because there are various structural analogues with tin-pnictide (SnPn) conducting layers, our results indicate that SnPn-based layered compounds can be categorized into a novel family of vdW-type superconductors, providing a new platform for studies on physics and chemistry of low-dimensional superconductors.

Crystal Structure and Electrical/thermal Transport Properties of Li1-xSn2+xP2 and Its Performance as a Li-Ion Battery Anode Material

“…No superconducting transition is observed down to 0.5 K, unlike for Na1-xSn2P2 and NaSn2As2. [17][18][19][20][21] The residual resistivity ratio (300 K)/(0.5 K) is estimated to be 1.3, which is comparable to those of related materials. [13][14][15]17,18,20,21,35 Due to the layered structure of Li1-xSn2+xP2, we investigated its anisotropy in resistivity with respect to uniaxial hot pressing direction above room temperature.…”

“…16 It has also been demonstrated that NaSn2As2 and Na1-xSn2P2 show superconducting transitions, meaning that these compounds can also be categorized as novel layered superconductors. [17][18][19][20][21] As well as these ternary-phase materials, the binary tin phosphide Sn4P3 has been investigated as a rechargeable battery anode material. [22][23][24][25][26][27][28][29][30][31] For example, the high reversible capacity of 850 mA•h•g −1 has been achieved for a Na-ion battery with a Sn4P3/C composite anode.…”

Ba2Si3P6: 1D Nonlinear Optical Material with Thermal Barrier Chains

“…For example, an incorporation of Li or Na into the interlayer space of binary tin phosphides and arsenides resulted in unexpected thermal and superconducting properties. [1][2][3] NaSn2As2 and Na1-xSn2P2 were shown to be superconductors at 1.3 K and 2.0 K respectively, revealing that Sn2Pn2 layers may be a basic layered building block exhibiting superconducting properties. 2,3 In ternary phases, tin atoms are octahedrally coordinated similar to the tin coordination in binary pnictides Sn4P3, Sn4As3, and Sn3P4.…”

“…[1][2][3] NaSn2As2 and Na1-xSn2P2 were shown to be superconductors at 1.3 K and 2.0 K respectively, revealing that Sn2Pn2 layers may be a basic layered building block exhibiting superconducting properties. 2,3 In ternary phases, tin atoms are octahedrally coordinated similar to the tin coordination in binary pnictides Sn4P3, Sn4As3, and Sn3P4. 4 Pnictides of lighter tetrels have different structural chemistry due to the tetra-coordinated nature of Si and Ge.…”

Synthesis, Crystal and Electronic Structure of La2SiP4

“…Metal tetrel‐pnictides ( A‐TtPn , A =electropositive metal, Tt =Si, Ge and Sn, Pn =P and As) are a large family of compounds showing a variety of crystal structures and atom connectivity, and exhibiting exciting transport, magnetic, and optical properties [1–9] . The underlying Tt‐Pn anionic sublattice can range from isolated TtPn 4 tetrahedra (Ca 4 SiP 4 , Sr 4 SiP 4 , Ba 4 SiP 4 , Li 8 SiP 4 and Li 8 GeP 4 ), 1D‐chains (Ca 3 Si 2 P 4 and K 2 SiP 2 ), 2D‐layers (LiGe 3 P 3 , LiGe 3 As 3 , Cs 0.16 SiAs 2 , Ca 2 Si 2 P 4 , Li 1‐x Sn 2 As 2 ), to 3D‐frameworks (Li 2 GeP 2 , SrSi 7 P 10 , BaSi 7 P 10 , Li 2 SiP 2 , LiSi 3 As 6 , MgSiAs 2 , Mg 3 Si 6 As 8 , and Ca 3 Si 8 P 14 ) [2,7,10–24] .…”