TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: A ratio of sodium to silicon used to form silicon containing sodium molecule is 10-30 mol.%, preferably 20 mol.%. In the method (M1), the mixture of sodium and silicon is heated in two steps, where in first step, the mixture is heated at 400 degrees C for 30 minutes, and in the second step, the mixture is heated at 800 degrees C for 1.5-24 hours. Preferred Components: The precursor: contains 24 silicon atoms and 4 sodium atoms; has a space group of Cmcm; and has lattice constants including a value of 4.106 Angstrom , b value of 10.563 Angstrom , and c value of 12.243 Angstrom . The orthorhombic allotrope of silicon has: a quasi-direct band gap with a direct gap value of 1.34 eV and an indirect gap value of 1.3 eV; an orthorhombic structure; a space group of Cmcm; and the lattice constants including a value of 3.83 Angstrom , b value of 10.69 Angstrom and c value of 12.63 Angstrom , where one unit cell contains 24 silicon atoms tetrahedrally bonded together. EXAMPLE - Mixture of sodium and silicon with 15 mol.% sodium was ground in a ceramic mortar for 1 hour inside a high-purity argon glovebox and loaded into a capsule. The capsule was then introduced in a 14/8 multi-anvil assembly using a re-heater and zirconia insulation. The mixture was pressurized in a 1500 ton multi-anvil press at a rate of 10 bar/hour (oil pressure) to a pressure of 10 GPa and reacted at 800 degrees C in two steps, where the mixture was preheated at 400 degrees C for 30 minutes to avoid a blow-out of the overheated sodium, and reaction was performed at the final temperature for 1 hour. Then the obtained sample was quenched by switching off the power. The recovered sample was easily removed from the capsule and washed with distilled water to obtain polycrystalline silicon containing sodium molecule (Na4Si24). Then the polycrystalline agglomerates of silicon containing sodium molecule were placed in a furnace under a dynamic vacuum of 10-5 Torr and degassed at 125 degrees C for 8 days to obtain the orthorhombic allotrope of silicon, which was subsequently washed thoroughly with water.