Structural Stability Diagram of ALnP₂S₆ Compounds (A = Na, K, Rb, Cs; Ln = Lanthanide)

Thiophosphate compounds have been studied extensively in the past for their rich structural variations and for a large variety of interesting properties. Here, we report 11 new phases with the composition ALnP₂S₆ (A = Na, K, Rb, Cs; Ln = lanthanide). These new thiophosphates crystallize in four different structure types, with the space groups <i>Fdd</i>2, <i>P</i>1̅, <i>P</i>2₁, and <i>P</i>2₁/<i>c</i>, respectively. All phases are insulating and the calculated band gaps range between 3 eV and 3.5 eV. Magnetic measurements on the compounds with open f-shells show paramagnetic behavior and magnetic moments that match the expected free ion values of the respective lanthanide cations. We present a structural stability phase diagram for the ALnP₂S₆ family of compounds, which reveals a clear relationship between ionic radii and the preferred crystal structure, as well as stability regions to form ALnP₂S₆-type phases

Copper Selenidophosphates Cu₄P₂Se₆, Cu₄P₃Se₄, Cu₄P₄Se₃, and CuP₂Se, Featuring Zero‑, One‑, and Two-Dimensional Anions

Five new compounds in the Cu/P/Se phase diagram have been synthesized, and their crystal structures have been determined. The crystal structures of these compounds comprise four previously unreported zero-, one-, and two-dimensional selenidophosphate anions containing low-valent phosphorus. In addition to two new modifications of Cu₄P₂Se₆ featuring the well-known hexa­selenido­hypodiphosphate­(IV) ion, there are three copper selenidophosphates with low-valent P: Cu₄P₃Se₄ contains two different new anions, (i) a monomeric (zero-dimensional) selenidophosphate anion [P₂Se₄]^4– and (ii) a one-dimensional selenidophosphate anion [P(−Se)]−∞1, which is related to the well-known gray-Se-like [P]−∞1 Zintl anion. Cu₄P₄Se₃ contains one-dimensional [P4(−Se)2]2−∞1 polyanions, whereas CuP₂Se contains the 2D selenidophosphate [P2(−Se)]−∞2 polyanion. It consists of charge-neutral CuP₂Se layers separated by a van der Waals gap which is very rare for a Zintl-type phase. Hence, besides black P, CuP₂Se constitutes a new possible source of 2D oxidized phosphorus containing layers for intercalation or exfoliation experiments. Additionally, the electronic structures and some fundamental physical properties of the new compounds are reported. All compounds are semiconducting with indirect band gaps of the orders of around 1 eV. The phases reported here add to the structural diversity of chalcogenido phosphates. The structural variety of this family of compounds may translate into a variety of tunable physical properties