Glass substrate for information recording medium

1. A glass substrate for an information recording medium, comprising the following glass components in % by weight:

SiO 2 : 52 to 67%;

Al 2 O 3 : 8 to 20%;

B 2 O 3 : 0 to 6% (including zero);

(wherein FMO=SiO 2 +Al 2 O 3 +B 2 O 3 =70 to 85%);

Li 2 O: 0.5 to 4%;

Na 2 O: 1 to 8%;

K 2 O: 0 to 5% (including zero);

(wherein R2O=Li 2 O+Na 2 O+K 2 O=5 to 15%);

MgO: 2 to 9%;

CaO: 0.1 to 5%;

BaO: 0 to 3% (including zero);

SrO: 0 to 3% (including zero);

ZnO: 0 to 5% (including zero);

(wherein MgO+CaO+BaO+SrO+ZnO=5 to 15%);

Y 2 O 3 : 0 to 4% (including zero);

La 2 O 3 : 0 to 4% (including zero);

Gd 2 O 3 : 0 to 4% (including zero);

CeO 2 : 0 to 4% (including zero);

TiO 2 : 1 to 7%;

HfO 2 : 0 to 2% (including zero);

ZrO 2 : 0 to 5% (including zero);

Nb 2 O 5 : 0.2 to 5%; and

Ta 2 O 5 : 0 to 5% (including zero); and

satisfying the following composition relation formulas (1) to (4):

Li 2 O/R2O:0.05 to 0.35  (1),

Li 2 O/FMO:0.005 to 0.035  (2),

Li 2 O/(MgO+ZnO):less than 2  (3) and

Nb 2 O 5 /SiO 2 :0.01 to 0.075  (4).

2. The glass substrate for an information recording medium according to claim 1 , exhibiting

Young's modulus E of 82 GPa or more and less than 90 GPa;

specific elastic modulus E/ρ of 31 or more when ρ is specific gravity;

Vickers hardness Hv of 550 to 650;

Li extraction amount A measured after a predetermined accelerated test, of 6 ppb or less per 2.5-inch disk; and

Si amount eluted in a predetermined elution test of 300 ppb or less per 2.5-inch disk.

3. The glass substrate for an information recording medium according to claim 1 , exhibiting glass transition point Tg of 550° C. or more and less than 650° C.

4. The glass substrate for an information recording medium according to claim 1 , exhibiting a coefficient of thermal expansion a of 45×10 −7 to 75×10 −7 /° C.

5. The glass substrate for an information recording medium according to claim 1 , exhibiting substantially uniform stress state on a main surface thereof.

6. The glass substrate for an information recording medium according to claim 1 , exhibiting heat conductivity β of 1 to 1.8 W/(mK).

7. The glass substrate for an information recording medium according to claim 1 , the content of Li 2 O is 0.8 to 3.5% by weight.

8. The glass substrate for an information recording medium according to claim 1 , wherein the glass substrate exhibits long term reliability.