Transparent ceramic, method for manufacturing same, and magneto-optical device
A transparent ceramic having terbium oxide (Tb 2 O 3 ) in a molar ratio of at least 40%; and at least one oxide selected among an yttrium oxide, a scandium oxide, and a lanthanide rare earth oxide, wherein (1) the crystal structure of the terbium-oxide-based ceramic does not contain a non-cubic-crystal phase, (2) the mean crystal particle diameter is in a range of 0.5 to 100 μm, and (3) the ceramic comprises a sintering auxiliary having no incidence of deposition of a non-cubic-crystal phase in the crystal structure of the terbium-oxide-based ceramic. This transparent ceramic makes a magneto-optical element that performs at least as well as terbium gallium garnet or other existing monocrystal materials. It also makes a functional element for an optical isolator in the infrared region between 500 nm and 1.5 μm having very little scattering and very few birefringence components.
1. A method for manufacturing a transparent ceramic material, comprising:
the first step (1) of grinding and mixing source powders including (a) terbium oxide, (b) at least one oxide selected from among yttrium oxide, scandium oxide, and a lanthanide rare earth oxide, and (c) a sintering aid which does not cause any heterophase but cubic to precipitate in the crystal structure of a terbium oxide-based ceramic material, said source powders (a) and (b) having same mean primary particle size of 30 to 2,000 nm,
the second step (2) of shaping the powder mix to form a green compact and calcining the green compact at 400 to 1,000° C. in an oxidizing atmosphere to form a calcined body, or calcining the powder mix at 400 to 1,000° C. in an oxidizing atmosphere and shaping the powder mix to form a calcined body,
the third step (3) of firing the calcined body at 1,400 to 1,700° C. in a non-oxidizing atmosphere to form a fired body, and
the fourth step (4) of pressure firing the fired body at 1,400 to 1,800° C. under a pressure of 19 to 196 MPa to form a pressure fired body.
2. The method of claim 1 , further comprising the step of annealing the pressure fired body at 1,500 to 2,000° C. in an oxygen-free atmosphere.
3. The method of claim 1 , wherein the sintering aid is an oxide, fluoride or nitride of an element selected from among titanium, zirconium, hafnium and calcium.
4. The method of claim 1 , wherein terbium oxide (chemical formula: Tb 2 O 3 ) (a) and the oxide (b) are provided that their total is 100 mol % in molar fraction, terbium oxide (a) is 40 to 60 mol %, with the balance being the oxide (b).