TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Compound: The compound (I) is preferably Sn0.7Li0.3P2O7, Sn0.95Li0.1P2O7, Sn0.8Li0.2P2O7, Sn0.6Li0.4P2O7, Sn0.5Li0.5P2O7, Sn0.7Na0.3P2O7, Sn0.7K0.3P2O7, Sn0.7Cs0.3P2O7, Zr0.9Li0.1P2O7, Ti0.9Li0.1P2O7, Si0.9Li0.1P2O7, Mo0.9Li0.1P2O7 or W0.9Li0.1P2O7. Preferred Method: The stirring is performed at 200-300 degrees C. The heat treating is performed at 300-1200 degrees C. Preferred components: The tetravalent metallic element precursor is selected from tin oxide, tin chloride, tin hydroxide, tungsten oxide, tungsten chloride, molybdenum oxide, molybdenum chloride, zirconium oxide, zirconium chloride, zirconium hydroxide, titanium oxide, and titanium chloride. The alkali metal precursor comprises at least one lithium hydroxide, lithium oxide, lithium chloride, lithium nitrate, sodium hydroxide, sodium chloride, potassium hydroxide, potassium chloride, cesium hydroxide or cesium chloride. The amount of phosphoric acid used is 200-300 parts by weight, based on 100 parts by weight of the tetravalent metallic element precursor. The solvent comprises deionized water.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The solvent comprises at least one methanol, ethanol or isopropyl alcohol. Preferred Definitions:    M=tin;    N1=lithium, sodium, potassium or cesium and    a=0.05-0.5.    EXAMPLE - Tin oxide, lithium hydroxide, and phosphoric acid (85 wt.%) were mixed together, in a molar ratio of Sn (tin):Li (lithium):P (phosphorus) of 0.7:0.3:2-3. De-ionized (ion exchange) water was added to the mixture, and the resultant was stirred at 250 degrees C to prepare a mixed paste having a high viscosity. The amount of lithium hydroxide was 30 mol %, and the amount of tin oxide was 70 mol%. The mixed paste was heat treated in an alumina crucible at 650 degrees C for 2.5 hours to form a lump of paste. The lump obtained after the heat treatment was pulverized with a mortar, to prepare a milk-white powder of Sn0.7Li0.3P2O7.