Zirconia sintered body

A zirconia sintered body comprising:

• a Y2O3 content in a total composition of the zirconia sintered body is 2.5 mol % or greater and 6 mol % or less, and a remainder comprising ZrO2 and unavoidable impurities, and having a relative density of 99% or greater, wherein
• in an electron microscopic observation image of a microstructure of the sintered body,
• an area-averaged grain size of zirconia crystal grains is 0.4 μm or greater and 0.9 μm or less,
• an area ratio of zirconia crystal grains with a grain size of less than 0.1 μm and an area ratio of zirconia crystal grains with a grain size exceeding 2 μm are both less than 1%,
• an area ratio of a first region configured by zirconia crystal grains with a grain size of 0.1 μm or greater and less than 0.5 μm is 5% or greater and 80% or less,
• an area ratio of a second region configured by zirconia crystal grains with a grain size of 0.8 μm or greater and less than 2 μm is 5% or greater and 80% or less,
• an area ratio of a third region configured by zirconia crystal grains with a grain size of 0.5 μm or greater and less than 0.8 μm is 10% or greater and less than 55%,
• an average Y2O3 concentration C2 of the zirconia crystal grains forming the second region is 3.5 mol % or greater and 7.0 mol % or less,
• an average Y2O3 concentration C1 of the zirconia crystal grains forming the first region is 1.7 mol % or greater and 5 mol % or less, and when a difference in the Y2O3 concentrations is denoted as ΔC≡C2−C1, a value of ΔC/C2 is 0.2 or greater and 0.5 or less, and
• a fracture toughness value measured by IF method is 4.5 MPa·m0.5 or greater and 12 MPa·m0.5 or less.