According to the present invention, there are provided a composite body that enables the formation of a lithium ion conductor that exhibits good lithium ion conductivity by a pressurization treatment without sintering at a high temperature (about 1,000° C.) while using a lithium-containing oxide having excellent safety and stability, as well as a lithium ion conductor, an all-solid state lithium ion secondary battery, an electrode sheet for an all-solid state lithium ion secondary battery, and lithium tetraborate. The composite body according to the embodiment of the present invention contains a lithium compound having a lithium ion conductivity of 1.0×10.sup.−6 S/cm or more at 25° C. and lithium tetraborate that satisfies the following requirement 1.

The requirement 1: In a reduced two-body distribution function G(r) obtained from an X-ray total scattering measurement of the lithium tetraborate, a first peak in which a peak top is located in a range where r is 1.43±0.2 Å and a second peak in which a peak top is located in a range where r is 2.40±0.2 Å are present, G(r) of the peak top of the first peak and G(r) of the peak top of the second peak indicate more than 1.0, and an absolute value of G(r) is less than 1.0 in a range where r is more than 5 Å and 10 Å or less.

According to the present invention, there are provided a composite body that enables the formation of a lithium ion conductor that exhibits good lithium ion conductivity by a pressurization treatment without sintering at a high temperature (about 1,000° C.) while using a lithium-containing oxide having excellent safety and stability, as well as a lithium ion conductor, an all-solid state lithium ion secondary battery, an electrode sheet for an all-solid state lithium ion secondary battery, and lithium tetraborate. The composite body according to the embodiment of the present invention contains a lithium compound having a lithium ion conductivity of 1.0×10.sup.−6 S/cm or more at 25° C. and lithium tetraborate that satisfies the following requirement 1.

The requirement 1: In a reduced two-body distribution function G(r) obtained from an X-ray total scattering measurement of the lithium tetraborate, a first peak in which a peak top is located in a range where r is 1.43±0.2 Å and a second peak in which a peak top is located in a range where r is 2.40±0.2 Å are present, G(r) of the peak top of the first peak and G(r) of the peak top of the second peak indicate more than 1.0, and an absolute value of G(r) is less than 1.0 in a range where r is more than 5 Å and 10 Å or less.

A lanthanum molybdenum composite oxide is provided. The lanthanum molybdenum composite oxide has a primary crystal phase formed of La.sub.2Mo.sub.2O.sub.9. The lanthanum molybdenum composite oxide also has a secondary crystal phase formed of a lanthanum molybdenum composite oxide species other than La.sub.2Mo.sub.2O.sub.9. The secondary crystal phase may contain at least one species selected from a group consisting of La.sub.2Mo.sub.3O.sub.12, La.sub.6MoO.sub.12, La.sub.7Mo.sub.7O.sub.30, La.sub.2Mo.sub.4O.sub.15, La.sub.2MoO.sub.6, La.sub.4MoO.sub.9, and LaMo.sub.2O.sub.5.

A lanthanum molybdenum composite oxide is provided. The lanthanum molybdenum composite oxide has a primary crystal phase formed of La.sub.2Mo.sub.2O.sub.9. The lanthanum molybdenum composite oxide also has a secondary crystal phase formed of a lanthanum molybdenum composite oxide species other than La.sub.2Mo.sub.2O.sub.9. The secondary crystal phase may contain at least one species selected from a group consisting of La.sub.2Mo.sub.3O.sub.12, La.sub.6MoO.sub.12, La.sub.7Mo.sub.7O.sub.30, La.sub.2Mo.sub.4O.sub.15, La.sub.2MoO.sub.6, La.sub.4MoO.sub.9, and LaMo.sub.2O.sub.5.

A light-emitting ceramic that includes a pyrochlore type compound that contains 0.01 mol % or more of Bi with respect to 100 mol % of the general formula M1.sub.XM2.sub.YM3.sub.ZO.sub.W, wherein M1 is at least one of La, Y, Gd, Yb, and Lu, M2 is at least one of Zr, Sn, and Hf, M3 is at least one of Ta, Nb, and Sb, X, Y, Z, and W are positive numbers that maintain electrical neutrality, X+Y+Z=2.0, 0.005≤Z≤0.2, and 3X+4Y+5Z is 7.02 or less.

A Faraday rotator and an optical isolator having a high transmittance and a high Verdet constant are provided. The optical isolator includes at least a Faraday rotator that rotates a polarization plane of incident light in a non-reciprocal manner, a polarizer disposed on a light incident side of the Faraday rotator, and an analyzer disposed on a light exit side of the Faraday rotator. The Faraday rotator is made of an oxide containing ytterbium oxide (Yb.sub.2O.sub.3), and is manufactured by a ceramic manufacturing process, wherein the oxide is allowed to contain an oxide of a metal other than ytterbium, and the proportion of ytterbium in all metal atoms in the oxide is 80% or more.

A Faraday rotator and an optical isolator having a high transmittance and a high Verdet constant are provided. The optical isolator includes at least a Faraday rotator that rotates a polarization plane of incident light in a non-reciprocal manner, a polarizer disposed on a light incident side of the Faraday rotator, and an analyzer disposed on a light exit side of the Faraday rotator. The Faraday rotator is made of an oxide containing ytterbium oxide (Yb.sub.2O.sub.3), and is manufactured by a ceramic manufacturing process, wherein the oxide is allowed to contain an oxide of a metal other than ytterbium, and the proportion of ytterbium in all metal atoms in the oxide is 80% or more.

A paramagnetic garnet-type transparent ceramic is a sintered body of complex oxide represented by the following formula (1), comprising SiO.sub.2 as a sintering aid in an amount of more than 0% by weight to 0.1% by weight or less, and has a linear transmittance of 83.5% or more at the wavelength of 1,064 nm for an optical path length of 25 mm:
(Tb.sub.1-x-yY.sub.xSc.sub.y).sub.3(Al.sub.1-zSc.sub.z).sub.5O.sub.12  (1)
wherein 0.05≤x<0.45, 0<y<0.1, 0.5<1−x−y<0.95, and 0.004<z<0.2.

A paramagnetic garnet-type transparent ceramic is a sintered body of complex oxide represented by the following formula (1), comprising SiO.sub.2 as a sintering aid in an amount of more than 0% by weight to 0.1% by weight or less, and has a linear transmittance of 83.5% or more at the wavelength of 1,064 nm for an optical path length of 25 mm:
(Tb.sub.1-x-yY.sub.xSc.sub.y).sub.3(Al.sub.1-zSc.sub.z).sub.5O.sub.12  (1)
wherein 0.05≤x<0.45, 0<y<0.1, 0.5<1−x−y<0.95, and 0.004<z<0.2.

A ceramic powder material containing a garnet-type compound containing Li, wherein the ceramic powder material has a pore volume of 0.4 mL/g or more and 1.0 mL/g or less.