Effects of transition metal (TM) substitution on the collapsed tetragonal transition in SrTM₂P₂

The dramatic reduction of the c-lattice parameter caused by a collapsed tetragonal transition gives rise to mechanical properties of technological interest, such as shape memory and a remarkable superelasticity [1]. This transition occurs in a wide variety of pnictide intermetallic compounds due to bond formation between pnictogens across ab planes. It is frequently found in P-T phase diagrams in proximity to different magnetic and/or superconducting transitions [2], and thus could potentially serve as a compass to find novel electronic and magnetic ground states. Motivated by this, we explore the case of SrNi₂P₂ which, upon cooling at ambient pressure, undergoes a transition into a partially collapsed structure, where only a third of the P ions bond across the Sr layers. We report on solution growth, transport and powder x-ray diffraction measurements to assess the effects that Co and Rh substitution have on this transition.

[1] Sypek et al., Nat. Commun. 8, 1083 (2017).

[2] Torikachvili et al., Phys. Rev. Lett., 101, 057006 (2008).