Potassium fluoride , crystal structure

Potassium fluoride and calcium oxide have the same crystal structure. Which one should melt at the higher temperature Explain why. 

Complex Fluorides of Platinum iv).— Although hexafluoroplatinic(iv) acid cannot be synthesized in water, its hydrolysis is so slow that the alkali, alkaline-earth, and rare-earth salts have aU been made from the acid in aqueous solution. The crystal structure of the potassium salt shows that the hexafluoroplatinate(iv) ion possesses the regular octahedral shape expected for a dizg electron configuration. 

Potassium fluoride, KF, has a rock-salt type of crystal structure. The density of KF is 2.468 g/cm. ... 

This structure type, that has been attributed to the fluorides KNbFa and KTaFs by Bode and Dohren [39, 40), is restricted in the case of potassium compounds KMeFe to the same transition elements Me + = Nb, Ta, Mo, W, Re (129), the sodium compounds NaMeFe of which adapt the NaSbFs structure. But as all AgMeFe-compounds 187) hitherto known seem to crystallize in the KNbFe-structure, this type is somewhat wider spread. 

Fig. 13-11.—The structure of the cubic crystal KMgF3. Potassium ions are represented by large shaded circles. They are at the corners of the unit cube. The fluoride ions, represented by large open circles, are at the face-centered positions, and the magnesium ions, represented by small circles, are at the center of the cubes. This structure is often called the perovskite structure perovskite is the mineral CaTiOj.

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