PROBLEM TO BE SOLVED: To provide a lanthanum hexaboride sintered body having a high relative density with which a lanthanum hexaboride film having a low work function can be obtained and a production method thereof.;SOLUTION: The sintered body is a lanthanum hexaboride sintered body in which lanthanum hexaboride and a rare earth metal boride with one or more electrons in 4f-orbitals are dissolved. Its oxygen element content is 1.0 mass% or less. Its carbon element content is 0.1 mass% or less. Its relative density is 88% or more. Its lattice constant is 4.1445Å or more and 4.1518Å or less. The production method for the lanthanum hexaboride sintered body comprises: a step (a) of treating a powder of lanthanum hexaboride and a powder of a rare earth metal boride with one or more electrons in 4f-orbitals with acid and obtaining a purified lanthanum hexaboride powder and a purified rare earth metal boride powder; and a step (b) of sintering a mixed powder of the purified lanthanum hexaboride powder and the purified rare earth metal boride powder obtained at the step (a) in one atmosphere selected from a reduction atmosphere and an inert gas atmosphere at 1700°C or higher under 10 MPa or higher.;COPYRIGHT: (C)2014,JPO&INPIT
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