Glass compositions include titania (TiO.sub.2), lanthanum oxide (La.sub.2O.sub.3) and boron oxide (B.sub.2O.sub.3) as essential components and may optionally include silica (SiO.sub.2), niobia (Nb.sub.2O.sub.5), zirconia (ZrO.sub.2), yttria (Y.sub.2O.sub.3), bismuth oxide (Bi.sub.2O.sub.3), tungsten oxide (WO.sub.3), zinc oxide (ZnO) and other components. The glasses may be characterized by high refractive index at 587.56 nm at comparably low density at room temperature.

Glass compositions include titania (TiO.sub.2), lanthanum oxide (La.sub.2O.sub.3) and boron oxide (B.sub.2O.sub.3) as essential components and may optionally include silica (SiO.sub.2), niobia (Nb.sub.2O.sub.5), zirconia (ZrO.sub.2), yttria (Y.sub.2O.sub.3), bismuth oxide (Bi.sub.2O.sub.3), tungsten oxide (WO.sub.3), zinc oxide (ZnO) and other components. The glasses may be characterized by high refractive index at 587.56 nm at comparably low density at room temperature.

Provided is an X-ray shielding glass having high shielding capability against X-rays with a tube voltage of 150 kV or less. The X-ray shielding glass has a composition including: 15 mass % to 25 mass % B.sub.2O.sub.3; 7 mass % to 50 mass % La.sub.2O.sub.3; 7 mass % to 50 mass % Gd.sub.2O.sub.3; 10 mass % to 25 mass % WO.sub.3; 0 mass % to 7 mass % SiO.sub.2; 0 mass % to 10 mass % ZrO.sub.2; 0 mass % to 8 mass % Nb.sub.2O.sub.5; 0 mass % to 10 mass % Ta.sub.2O.sub.5; 0 mass % to 5 mass % Bi.sub.2O.sub.3; 0 mass % to 3 mass % CeO.sub.2; and 0 mass % to 1 mass % Sb.sub.2O.sub.3, wherein the glass contains no ZnO, the total content of La.sub.2O.sub.3 and Gd.sub.2O.sub.3 is 45 mass % to 65 mass %, and when the thickness of the glass is 3 mm, the transmittance of the glass to an X-ray from an X-ray tube with a tube voltage of 60 kV is 0.0050% or less, and the transmittance of the glass to an X-ray from an X-ray tube with a tube voltage of 100 kV is 0.1500% or less.

Provided is an X-ray shielding glass having high shielding capability against X-rays with a tube voltage of 150 kV or less. The X-ray shielding glass has a composition including: 15 mass % to 25 mass % B.sub.2O.sub.3; 7 mass % to 50 mass % La.sub.2O.sub.3; 7 mass % to 50 mass % Gd.sub.2O.sub.3; 10 mass % to 25 mass % WO.sub.3; 0 mass % to 7 mass % SiO.sub.2; 0 mass % to 10 mass % ZrO.sub.2; 0 mass % to 8 mass % Nb.sub.2O.sub.5; 0 mass % to 10 mass % Ta.sub.2O.sub.5; 0 mass % to 5 mass % Bi.sub.2O.sub.3; 0 mass % to 3 mass % CeO.sub.2; and 0 mass % to 1 mass % Sb.sub.2O.sub.3, wherein the glass contains no ZnO, the total content of La.sub.2O.sub.3 and Gd.sub.2O.sub.3 is 45 mass % to 65 mass %, and when the thickness of the glass is 3 mm, the transmittance of the glass to an X-ray from an X-ray tube with a tube voltage of 60 kV is 0.0050% or less, and the transmittance of the glass to an X-ray from an X-ray tube with a tube voltage of 100 kV is 0.1500% or less.

A joint joins an alloy member to a ceramic member via a glass joining agent, which is joined to the alloy member by a material bonded joint and to the ceramic member by a further material bonded joint. The glass joining agent is made of a glass having a melting point below 800° C.; a coefficient of thermal expansion of at least 9-10.sup.−6 K.sup.−1 and a bismuth content of at least 10%. The alloy member has a coefficient of thermal expansion of at least 9-10.sup.−6 K.sup.−1. The ceramic member has a maximum coefficient of thermal expansion of 8-10.sup.−6 K.sup.−1. The material bonded joint defines a mixing region that is a partial region of the ceramic member, and the bismuth content in the mixing region is higher than that of the ceramic member outside the mixing region.

An optical glass includes, in terms of mol % of cations, a total amount of La.sup.3+, Y.sup.3+, and Gd.sup.3+ components falling within a range of from 5% to 65% and a total amount of Zr.sup.4+, Hf.sup.4+, and Ta.sup.5+ components falling within a range of from 5% to 65%, and a relationship expressed in Expression (1) given below is satisfied. (La.sup.3++Y.sup.3++Gd.sup.3+)×(Zr.sup.4++Hf.sup.4++Ta.sup.5+)≥400 (%).sup.2

Glasses containing silicon dioxide (SiO.sub.2) and/or boron oxide (B.sub.2O.sub.3) as glass formers and having a refractive index n.sub.d of greater than or equal to 1.9, as measured at 587.56 nm, and a density of less than or equal to 5.5 g/cm.sup.3, as measured at 25° C., are provided. Optionally, the glasses may be characterized by a high transmittance in the visible and near-ultraviolet (near-UV) range of the electromagnetic spectrum and/or good glass forming ability.

To provide an optical glass having the optical characteristics of a high refractive index and low dispersion, and moreover, which makes it possible to further reduce devitrification and which can be stably obtained, and a preform and an optical element using the same. The optical glass comprises, expressed in cation % (mol %), 17.0% to 42.0% of P.sup.5+, 7.0% to 30.0% of Al.sup.3+, more than 0% to 22.0% of Mg.sup.2+, more than 0% to 25.0% Ca.sup.2+, more than 0% to 30.0% of Sr.sup.2+, more than 0% to 35.0% Ba.sup.2+, and expressed in anion % (mol %), a content ratio of F.sup.− of 37.0 to 64.0%, a content ratio of O.sup.2− of 36.0 to 63.0%, a refractive index (nd) of 1.48 to 1.58, and having an Abbe number (vd) of 70 to 88, and a liquidus temperature of 800° C. or less.

To provide an optical glass having the optical characteristics of a high refractive index and low dispersion, and moreover, which makes it possible to further reduce devitrification and which can be stably obtained, and a preform and an optical element using the same. The optical glass comprises, expressed in cation % (mol %), 17.0% to 42.0% of P.sup.5+, 7.0% to 30.0% of Al.sup.3+, more than 0% to 22.0% of Mg.sup.2+, more than 0% to 25.0% Ca.sup.2+, more than 0% to 30.0% of Sr.sup.2+, more than 0% to 35.0% Ba.sup.2+, and expressed in anion % (mol %), a content ratio of F.sup.− of 37.0 to 64.0%, a content ratio of O.sup.2− of 36.0 to 63.0%, a refractive index (nd) of 1.48 to 1.58, and having an Abbe number (vd) of 70 to 88, and a liquidus temperature of 800° C. or less.

A glass frit includes Bi.sub.2O.sub.3 and has a glass transition temperature (Tg) in a range of 280° C. to 320° C. A display device includes the glass frit including Bi.sub.2O.sub.3 and the glass transition temperature (Tg) in the range of 280° C. to 320° C. The display device shows excellent internal reliability and drop strength.