Extending the n=2 Ruddlesden-Popper solid solution La2-2xSr1+2xMn2O7 beyond x=0.5: synthesis of Mn4+-rich compounds

Reported herein are the synthesis and room temperature crystal structures o f the heretofore unknown, metastable manganites La2-2xSr1 + 2xMn2O7 + delta (0.5 less than or equal to x less than or equal to 0.9) via high temperatu re (T = 1650 degrees C) quenching followed by low temperature (T = 400 degr ees C) annealing to fill oxygen vacancies; this approach enables access to the electronic, magnetic, and structural properties of previously unexplore d compositions in this important CMR system.