The present invention provides polycrystalline silicon suitably used as a raw material for producing single crystal silicon. The polycrystalline silicon rod of the present invention is a polycrystalline silicon rod grown by chemical vapor deposition performed under a pressure of 0.3 MPaG or more, wherein when a plate-shaped sample piece collected from an arbitrary portion of the polycrystalline silicon rod is observed with a microscope with a temperature increased from a temperature lower than a melting point of silicon up to a temperature exceeding the melting point of silicon, a heterogeneous crystal region, which is a crystal region including a plurality of crystal grains heterogeneously assembled and including no needle-like crystal, having a diameter exceeding 10 m is not observed.

The present invention provides polycrystalline silicon suitably used as a raw material for producing single crystal silicon. The polycrystalline silicon rod of the present invention is a polycrystalline silicon rod grown by chemical vapor deposition performed under a pressure of 0.3 MPaG or more, wherein when a plate-shaped sample piece collected from an arbitrary portion of the polycrystalline silicon rod is observed with a microscope with a temperature increased from a temperature lower than a melting point of silicon up to a temperature exceeding the melting point of silicon, a heterogeneous crystal region, which is a crystal region including a plurality of crystal grains heterogeneously assembled and including no needle-like crystal, having a diameter exceeding 10 m is not observed.

Provided is a novel production method for producing silicon clathrate II. In the production method for producing silicon clathrate II, in a reaction system in which a NaSi alloy containing Na and Si and an Na getter agent coexist so as not to be in contact with each other, the NaSi alloy is heated and Na evaporated from the NaSi alloy is thus caused to react with the Na getter agent to reduce an amount of Na in the NaSi alloy.

Provided is a novel production method for producing silicon clathrate II. In the production method for producing silicon clathrate II, in a reaction system in which a NaSi alloy containing Na and Si and an Na getter agent coexist so as not to be in contact with each other, the NaSi alloy is heated and Na evaporated from the NaSi alloy is thus caused to react with the Na getter agent to reduce an amount of Na in the NaSi alloy.

In an embodiment of the present invention, contaminants contained in polycrystalline silicon are removed to obtain highly-pure polycrystalline silicon, with only a small amount of etching. Polycrystalline silicon is washed with use of: a first washing step of bringing fluonitric acid into contact with the polycrystalline silicon; and a second washing step of bringing a non-oxidizing chemical containing hydrofluoric acid into contact with the polycrystalline silicon that has undergone the first washing step.

In an embodiment of the present invention, contaminants contained in polycrystalline silicon are removed to obtain highly-pure polycrystalline silicon, with only a small amount of etching. Polycrystalline silicon is washed with use of: a first washing step of bringing fluonitric acid into contact with the polycrystalline silicon; and a second washing step of bringing a non-oxidizing chemical containing hydrofluoric acid into contact with the polycrystalline silicon that has undergone the first washing step.

A silicon granule, in particular, for the preparation of trichlorosilane, having a size of between 10 and 500 microns, and comprising: dopants in a weight fraction of less than 5 ppm; at least one co-catalyst selected from copper, iron, aluminum and calcium, in a weight fraction of between 1 and 2500 ppm; and metallic impurities, with exclusion of the at least one co-catalyst, in a weight fraction of less than 50 ppm.

Provided are a negative electrode active material for a secondary battery, which suppresses a dispersal phenomenon of a negative electrode active material during charging/discharging by controlling a lattice mismatch ratio of an amorphous matrix layer to a silicon layer in a silicon-based negative electrode active material.

Provided are a negative electrode active material for a secondary battery, which suppresses a dispersal phenomenon of a negative electrode active material during charging/discharging by controlling a lattice mismatch ratio of an amorphous matrix layer to a silicon layer in a silicon-based negative electrode active material.

A hood for a taphole and a tapping spout in a submerged arc furnace in the production of silicon. The hood has at least two suction ducts which are placed asymmetrically on either side of the hood, and is useful in a process for the production of silicon in a submerged arc furnace, wherein liquid silicon and refining gas escape from a taphole of a crucible, wherein the liquid silicon flows on a tapping spout into a ladle, wherein the refining gas is sucked in a hood which has at least two suction ducts which are placed on either side of the hood.