Polymorphism and physical properties of LnNi2As2 compounds (Ln = La → Gd)

Structure phase transitions of polymorphic compounds with layered crystal structures: The REIr2Si2 case

“…In this manuscript we address the REIr 2 Si 2 (RE ¼ La, Ce, Pr, Nd and Yb) [1e5], but the RENi 2 As 2 compounds (RE ¼ La, Ce, Pr, Nd, Sm) [6] may serve as additional examples. These compounds can crystallize either in the high-temperature b-phase (tetragonal CaBe 2 Ge 2 -type, space group P4/nmm) or in the low-temperature a-phase (ThCr 2 Si 2 -type, space group I4/mmm) which differ by the stacking of the atoms along the c-axis (see Fig.…”

Polymorphism of PrIr2Si2 – In situ XRPD experiments and theoretical calculations

“…As examples may serve the RENi 2 As 2 (RE ¼ La, Ce, Pr, Nd, Sm), LaIr 2 Si 2 , CeIr 2 Si 2 and NdIr 2 Si 2 [1][2][3] compounds. For PrIr 2 Si 2 , however, only the ThCr 2 Si 2 -type crystallographic structure [4] can be found in literature.…”

Superconductivity in LaPd2As2 with a collapsed 122 structure

“…T c (K) Materials (A = alkaline earth) T c (K) LaFe 2 P 2 (ucT) 22 (1.80) CaFe 2 P 2 (cT) 22 (1.80) SrFe 2 P 2 (ucT) 22 BaFe 2 P 2 (ucT) 22 LaRu 2 P 2 (ucT) 6 4.10 CaRu 2 P 2 (cT) 6 (1.80) SrRu 2 P 2 (ucT) 6 BaRu 2 P 2 (ucT) 6 LaCo 2 As 2 (cT) 24 (2.00) CaCo 2 As 2 (cT) 27,28 (1.8) SrCo 2 As 2 (ucT) 27,29 (1.30) BaCo 2 As 2 (cT) 21,30 (1.8) LaCo 2 P 2 (cT) 24 (2.00) CaCo 2 P 2 (cT) 31 (2) SrCo 2 P 2 (cT) 32 (1) LaNi 2 As 2 (cT) 10 (2.00) CaNi 2 As 2 (cT) 33 (2) SrNi 2 As 2 (cT) 34 0.62 BaNi 2 As 2 (ucT) 35 0.70 LaRu 2 As 2 (cT) 6 (1.8) CaRu 2 As 2 (cT) 6 (1.80) SrRu 2 As 2 (cT) 6 BaRu 2 As 2 (ucT) 6 LaNi 2 P 2 (cT) 25 (5) CaNi 2 P 2 (cT) 25,26 (1.80) SrNi 2 P 2 (ucT) 36 1.40 BaNi 2 P 2 (ucT) 37 3.00…”

“…However, as pointed out by Hoffmann and Zheng [7], interlayer X-X bonding sometimes forms to give a 3D network, called a collapsed tetragonal (cT) structure. The Ba, Sr and Ca-based series of iron arsenides remain in the un-collapsed tetragonal (ucT) structure at ambient pressure, while SrCu 2 As 2 , CaCu 1.7 As 2 , CaPd 2 As 2 , SrPd 2 As 2 and LaNi 2 As 2 crystallize in the cT structure [8][9][10].…”