ABOUT THE EFFECT OF TEMPERATURE, PRESSURE, AND SUBSTITUTION ON THE CRYSTAL-STRUCTURE OF ARH(2)P(2) (A = CA, SR, EU, BA)

Four compounds ARh(2)P(2) (A = Ca, Sr, Eu, Ba) were prepared by heatin g mixtures of the elements and investigated by means of single crystal X-ray methods. They crystallize in the ThCr2Si2 type structure (I4/mm m; Z = 2) with P-P distances along [001] reaching from 2.26 Angstrom ( CaRh2P2) to 3.74 Angstrom (BaRh2P2). With increasing temperature (EuRh 2P2) or increasing pressure (SrRh2P2) a first order phase transition o ccurs with strong changes of the P-P distances. Substitution of the at oms changes the bond lengths of the compounds too.