Phase transformation and functional behavior of Na2MP2O7 (M = Mn, Co) pyrophosphates

A range of inorganic materials, with structures based on transition metal (TM) centeredpolyhedra linked through polyanionic units, have been reported with a wide variety of applications. Depending upon the TM cation coordination geometry and the surrounding ligand anions, such inorganic materials may exhibit wide structural diversity and polymorphism. One such family of compounds is disodium metal pyrophosphates (Na2MP2O7), which is formed by a condensation reaction of two inorganic phosphate units. The pyrophosphate (P2O7)4- based systems exhibit rich crystal chemistry and play critical role in a wide range of applications such as energy storage, ionic conductivity and near infrared absorption (NIR) depending upon the constituent transition metals. In the present work, we have studied Mn and Co-based pyrophosphates, where we have noticed ‘phase transformation’ depending on the synthesis methods/ conditions. Polymorphs of Na2MnP2O7 and Na2CoP2O7 were characterized by diffraction analyses. Their functional properties have been explored by synergizing electrochemical testing methods along with the bond valence site energy (BVSE) modeling to investigate their ionic conductivity, electrocatalytic and electrochemical performance.A range of inorganic materials, with structures based on transition metal (TM) centeredpolyhedra linked through polyanionic units, have been reported with a wide variety of applications. Depending upon the TM cation coordination geometry and the surrounding ligand anions, such inorganic materials may exhibit wide structural diversity and polymorphism. One such family of compounds is disodium metal pyrophosphates (Na2MP2O7), which is formed by a condensation reaction of two inorganic phosphate units. The pyrophosphate (P2O7)4- based systems exhibit rich crystal chemistry and play critical role in a wide range of applications such as energy storage, ionic conductivity and near infrared absorption (NIR) depending upon the constituent transition metals. In the present work, we have studied Mn and Co-based pyrophosphates, where we have noticed ‘phase transformation’ depending on the synthesis methods/ conditions. Polymorphs of Na2MnP2O7 and Na2CoP2O7 were characterized by diffraction analyses. Their functional...