Average ionic radius for element (with units). The average is taken
        over all oxidation states of the element for which data is present.

def average_ionic_radius(self):
        """
        Average ionic radius for element (with units). The average is taken
        over all oxidation states of the element for which data is present.
        """
        if "Ionic radii" in self._data:
            radii = self._data["Ionic radii"]
            return sum(radii.values()) / len(radii)
        else:
            return 0