Magnetic, structural, and Raman characterization of R${\mathrm{Ba}}_2$${\mathrm{Cu}}_2$${\mathrm{NbO}}_8$(R=Pr, La, or Nd)

${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{NbO}}_8$ (PrBCNO) is an insulator analogous to the ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ system having a similar structure but with ${\mathrm{NbO}}_2$ planes replacing the CuO chains. Single-phase polycrystalline samples of RBCNO have been synthesized with R=La, Pr, or Nd. These materials were characterized using magnetization, thermal gravimetric analysis in different atmospheres, x-ray diffraction, and Raman spectroscopy. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12 K. No such magnetic phase transition is observed down to 2 K in ${\mathrm{NdBa}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{NbO}}_8$.