JP2003286070A - Semiconducting ceramic and holding member and tool for magnetic disk substrate using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconducting ceramic constituted so that bending strength, Young's modulus, hardness and fracture toughness which affect the workability are controlled to have a value in a suitable range, prescribed semiconductivity and a coefficient of thermal expansion are attained and such inconvenience that the chipping easily occurs by various shocks is reduced and durability is improved in the semiconducting ceramic having 2MgO.SiO<SB>2</SB>(forstelite) as an essential crystal phase and iron oxide as a sub-component, and to provide holding member and tool for a magnetic disk substrate using the semiconducting ceramic. <P>SOLUTION: The semiconducting ceramic is composed of a sintered compact having 2MgO.SiO<SB>2</SB>as an essential crystal phase and at least one kind of a crystal selected from MgFe<SB>2</SB>O<SB>4</SB>, Fe<SB>3</SB>O<SB>4</SB>and Fe<SB>2</SB>O<SB>3</SB>and the crystal of MgO as sub-components. The holding members (a spacer 12, a shim 11 and clamp 13) and tools for the magnetic disk substrate use the semiconducting ceramic. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductive ceramic, a magnetic disk substrate holding member such as a spacer, a shim, a hub and the like for holding a plurality of magnetic disk substrates at predetermined intervals using the same and jigs. Regarding

[0002]

2. Description of the Related Art Conventionally, as conductive ceramics, alumina, zirconia or the like has been used as a main component, and metals such as Ni, Nb, Co, Ti, Zr, Ta and Hf or their compounds as conductivity imparting materials or their compounds are used as ceramic materials. A sintered body is known which is added and burned. These conductive ceramics have been used as a static electricity removing member such as a ceramics sensor, a separating claw of a printer, a member for an electronic component manufacturing apparatus, a resistance substrate, etc. (Japanese Patent Laid-Open No. 2-2950).
09, etc.).

On the other hand, a magnetic recording device is used as a recording means of a computer, and a static electricity removing member is also used in this magnetic recording device. FIG. 1 is a schematic sectional view of a magnetic recording device. As shown in the figure, in this magnetic recording apparatus 10, a plurality of magnetic disk substrates 16 made of glass and spacers 12 are alternately attached to a hub 15 fixed to a rotating shaft 14 and pressed by shims 11 and clamps 13. After that, the structure is such that it is fixed by tightening with a screw 17.

In order to read and write information, the rotating shaft 14 is rotated by a motor (not shown), and the hub 1
The magnetic heads 18 on the magnetic disk substrate 16 are levitated by rotating the plurality of magnetic disk substrates 16 fixed on the magnetic disk substrate 5 at a high speed.
Information is written or read at a predetermined position on the magnetic disk substrate 16 by scanning on the magnetic disk 6.

However, when the magnetic disk substrate 16 is charged, the information written at the time of discharging is destroyed, so the spacer 1 for holding the magnetic disk substrate 16 at a predetermined interval.
It has been proposed to form the magnetic disk substrate holding member such as 2, the shim 11, the clamp 13 or the like with a conductive material. As the conductive material forming the magnetic disk substrate holding member, a titania-based sintered body or titanium oxide is used. (Ti
O ₂ ), titanium carbide (TiC), tin oxide (SnO, Sn)
A conductive ceramic such as an alumina-based sintered body containing O ₂ ) has been used (see JP-A-6-168536 and JP-A-11-228224).

[0006] However, in the case of a conductive ceramic comprising a sintered body containing alumina or zirconia as a main component and a conductivity-imparting material added thereto, the conductivity-imparting material is expensive and must be fired in a reducing atmosphere. Since it requires special firing conditions such as not happening, it has been very difficult to commercialize it while there is a demand for cost reduction.

Further, in a magnetic disk substrate holding member made of a sintered body containing alumina or zirconia as a main component or a titania-based sintered body, 2 to 5 × 10 ⁻⁶ / is provided between the magnetic disk substrate made of glass and the magnetic disk substrate. Since there is a difference in coefficient of thermal expansion of about ℃,
There are problems that the magnetic disk substrate 16 is distorted due to heat generated during operation, and the flatness between the magnetic disk substrates 16 is impaired.

In order to solve these problems, the present inventors have previously made a semi-conductive ceramic composed of a sintered body containing forsterite as a main component and iron oxide added as a conductivity-imparting material, It has been proposed to form a holding member for a magnetic disk substrate from this semi-conductive ceramic (Japanese Patent Laid-Open No. 9-20560, Patent 29841).
99, Japanese Patent Laid-Open No. 11-343169).
The semiconductive ceramics in these proposals are 2Mg
Has O.SiO ₂ and MgSiO ₃ crystals, and MgFe
_It has at least one kind of crystal of ₂ O ₄ and Fe ₃ O ₄ , and has a volume resistivity value of 10 ⁷ Ω · cm or less, a bending strength of 100 to 140 MPa, and a Young's modulus of 100 to 140.
It was about GPa.

The semiconductive ceramics made of a sintered body containing forsterite as a main component and iron oxide as a conductivity-imparting material is reacted with Mg as a main component, MgFe ₂ O ₄ and unreacted. It has been clarified that the amount of iron oxide contributes to the conductivity, and compared with the above-mentioned conductive ceramics containing alumina or zirconia as the main component, the added amount of iron oxide and the crystalline phase having conductivity. From the relationship with the peak intensity of X-ray diffraction of (MgFe ₂ O ₄ and unreacted iron oxide), it is easy to adjust the volume resistivity, and 10 ⁴ to 10 ⁷ Ω · cm required for the static electricity removing member can be obtained. In addition to being satisfied, the main components of forsterite are MgO and Si.
O ₂ composite oxide, glass magnetic disk substrate 16
Since the coefficient of thermal expansion can be approximated to the above, there is an advantage that thermal strain is prevented from occurring in the magnetic disk substrate 16 and the flatness between the magnetic disk substrates 16 can be maintained with high accuracy.

[0010]

In recent years, as the recording density of the magnetic disk device 10 has become higher and higher, the floating gap between the magnetic head 18 and the magnetic disk substrate 16 has been minimized. Currently, the floating gap is less than 0.02 μm. It is a small area. When the levitation gap is minimized in this way, the shim 11 for fixing the magnetic disk substrate 16 in order to maintain the flatness between the magnetic disk substrates 16 with higher accuracy,
There has been a growing demand for further improving the processing accuracy of the spacer 12, the clamp 13, and the hub 15 itself.
Further, in addition to the above-mentioned problem of processing accuracy, there is a problem that cracks are likely to occur in the sintered body due to various impacts.

[0011]

OBJECT OF THE INVENTION The object of the present invention is to obtain 2MgO.SiO.
₂ (Forsterite) as a main crystal phase and iron oxide as a sub-component in a semiconductive ceramic, the bending strength, Young's modulus, hardness and fracture toughness value that affect workability are set in a more preferable range, and Semi-conductive ceramics capable of obtaining semi-conductivity and coefficient of thermal expansion, further reducing defects such as chipping easily caused by various impacts, and improving durability, and a magnetic disk substrate using the same To provide a holding member and a jig.

[0012]

The inventors of the present invention have conducted extensive studies to solve the above problems relating to processing accuracy and durability, and as a result, 2MgO.SiO ₂ (forsterite)
In a semi-conductive ceramic having as a main crystal phase and iron oxide as a subcomponent, 2MgO.Si is contained in this sintered body.
By discovering not only O ₂ but also MgO, the new fact that the mechanical properties that affect the workability of the sintered body can be made into a more suitable range was found, and the present invention was completed. It was

That is, the semiconductive ceramic according to the present invention has 2MgO.SiO ₂ as a main crystal phase and at least one kind selected from MgFe ₂ O ₄ , Fe ₃ O ₄ and Fe ₂ O ₃ as a sub crystal phase. It is characterized by comprising a sintered body having crystals and MgO crystals.

In the semiconductive ceramic of the present invention, when the peak intensity at 2θ = 43 ° of the MgO crystal phase obtained by analyzing the semiconductive ceramic by X-ray diffraction is 1, MgFe ₂ O ₄ , Fe ₃ O ₄ and Fe ₂ O ₃
It is preferable that the peak intensity in the vicinity of 2θ = 35 to 36 ° (hereinafter, referred to as “peak intensity ratio”) in which the crystal phases of (2) are mixed is 0.2 to 4.

In the semiconductive ceramic of the present invention, Mg contained in the semiconductive ceramic is Mg.
40 to 68% by weight in terms of O, Si is 1 in terms of SiO _2.
4.5 to 30% by weight, Fe is 10 to 40 in terms of Fe ₂ O _3.
It is preferably wt%.

Further, in the semiconductive ceramic of the present invention, the volume resistivity of the semiconductive ceramic is 10 ⁴
It is preferable that it is -10 ⁷ Ω · cm, bending strength is 150 MPa or more, Young's modulus is 200 GPa or more, hardness is 8 GPa or more, and fracture toughness value is 1.5 MPa · m ^0.5 or more.

A holding member for a magnetic disk substrate according to the present invention is a holding member for holding the magnetic disk substrate at a predetermined position, and is formed of the semiconductive ceramic and has a contact surface with the magnetic disk substrate. Has a flatness of 3
It is characterized by being less than or equal to μm.

A jig / tool according to the present invention is characterized by being formed of the semiconductive ceramic.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. The conductive ceramics according to the present invention include 2MgO.SiO ₂ as a main crystal phase and at least one crystal selected from MgFe ₂ O ₄ , Fe ₃ O ₄ and Fe ₂ O ₃ as a sub-crystal phase and a MgO crystal. And a sintered body having

The main crystal phases 2MgO.SiO ₂ (forsterite) and MgO are insulating ceramics having a high volume resistivity value. Iron oxide (FeO, Fe _{2) is} used as a conductivity-imparting material for the insulating ceramics. O ₃ , Fe
By adding ₃ O ₄ ), semiconductivity can be imparted, and the volume resistivity value can be made 10 ⁴ to 10 ⁷ Ω · cm required for the static electricity removing member.

By thus containing iron oxide, the semiconductive ceramic of the present invention contains 2MgO.
Crystals of SiO ₂ and MgO and at least one crystal selected from MgFe ₂ O ₄ , Fe ₃ O ₄ and Fe ₂ O ₃ are present. Further, the peak intensity ratio by X-ray diffraction of this semiconductive ceramic is preferably 0.2 to 4.

When the peak strength ratio is in the range of 0.2 to 4, the flexural strength, Young's modulus, hardness and other rigidity and fracture toughness of the ceramic can be improved. As a result, it is possible to further improve the processing accuracy of the surface of the member by grinding and polishing for processing the sintered body into the shape of a holding member for magnetic disk substrates or jigs and tools. It is possible to minimize the distortion due to the tightening force of the disk, the centrifugal force during rotation, and the heat generated by the motor when the magnetic disk substrate is rotated at a high speed. Further, due to the improved rigidity, even when the semiconductive ceramic of the present invention is used as a holding member for a magnetic disk substrate of a hard disk device of a notebook type personal computer, various impacts caused when carrying the sintered product will cause a change in the sintered body. The occurrence of chipping is greatly reduced, and the durability is further improved.

On the other hand, the peak intensity ratio is 0.2
If it is less than MgFe which has conductivity in the sintered body
_The amount of crystals such as ₂ O ₄ , Fe ₃ O ₄ , Fe ₂ O _{3 and the} like is reduced, which may make it impossible to obtain a desired volume resistivity value. On the other hand, when the peak intensity ratio exceeds 4, it is considered that Mg contributes to the improvement of mechanical properties of the sintered body.
There is a possibility that the amount of O crystals present decreases and it becomes impossible to improve bending strength, Young's modulus, hardness, fracture toughness and the like. That is, not only 2MgO.SiO ₂ crystals but also MgO crystals are precipitated in the sintered body, and M which has excellent rigidity.
By newly presenting the gO crystal in the form of being dispersed in the sintered body, the mechanical properties that affect the processing accuracy of the sintered body by grinding and polishing, and the durability of the sintered body against impact, namely, It is presumed that the values of bending strength, Young's modulus, hardness and fracture toughness can be improved.

In the semiconductive ceramic of the present invention, Mg contained in the semiconductive ceramic is Mg.
It is preferably 40 to 68% by weight in terms of O for improving the mechanical properties, and more preferably 44 to 65% by weight. At this time, it is preferable that Si contained in the semiconductive ceramic is 14.5 to 30% by weight in terms of SiO ₂ and Fe is 10 to 40% by weight in terms of Fe ₂ O ₃ .

Since Fe contained in the semiconductive ceramic is 10 to 40% by weight in terms of Fe ₂ O ₃ ,
A volume resistivity value in the range of 0 ⁴ to 10 ⁷ Ω · cm can be obtained. When Fe is less than 10% by weight in terms of Fe ₂ O ₃ , the desired volume resistivity cannot be obtained, and when it exceeds 40% by weight, a large amount of iron oxide crystal phase is present in the ceramic, which causes bending. Mechanical properties such as strength may decrease. Further, in order to further improve the characteristics of ceramics, Fe is 15 to 35% by weight in terms of Fe ₂ O _3.
It is more preferable to add it so as to be within the range.

In the semiconductive ceramics of the present invention, crystals of 2MgO.SiO ₂ and MgO, MgFe
_At least 1 selected from ₂ O ₄ , Fe ₃ O ₄ and Fe ₂ O ₃
In addition to the seed crystal, MgSiO ₃ (steatite) may be included as a crystal phase.

Further, in the conductive ceramics of the present invention, M
In addition to g, Si, Fe, O components, Al, Ti, Ca, M
Impurities such as n and S may be contained in the form of a compound such as an oxide or a nitride in an amount of 1% by weight or less of the whole ceramic.

Next, a method of manufacturing the semiconductive ceramic according to the present invention will be described. First, commercially available MgO or its compound or hydrate, silica composite oxide (for example, talc (Mg ₃ Si ₄ O ₁₀ (OH) ₂ )), and iron oxide (FeO, Fe ₂ O ₃ , Fe ₃ O ₄ ) The respective powders are mixed in a predetermined weight. At this time, in order to precipitate a crystal phase of MgO in the sintered body after firing and improve mechanical properties, the molar ratio of MgO / SiO ₂ in the sintered body is larger than 2, preferably 3 or more. The amount of MgO or its compound, hydrate, and silica composite oxide added is adjusted so that When this molar ratio is 2 or less, Mg is contained in the sintered body.
O does not precipitate.

Then, a binder such as water or a water-soluble binder (polyvinyl alcohol, polyethylene glycol, acrylic resin, etc.) is added to the above-mentioned mixed powder, and the mixture is pulverized and mixed for 12 hours or more with a ball mill or the like, and the obtained slurry is discharged. to recover. Then, this slurry is granulated by a granulation method such as a spray dryer in a form including a binder to obtain a moldable powder, which is then molded into a predetermined shape using a press molding method or the like, and the temperature of 1500 to 1700 ° C. By firing at a firing temperature for 1 to 2 hours, the semiconductive ceramic of the present invention is obtained.

Here, the above-mentioned MgO / SiO ₂ molar ratio is set to 3 or more because if the molar ratio is 3 or more, M
This is because gO crystals can be precipitated to more stably improve the mechanical properties of the sintered body. Further, the molar ratio is more preferably in the range of 3 to 5 in order to suppress the MgO ratio and keep the firing temperature low to facilitate the production.

Although the pulverization and mixing time is set to 12 hours or more, the pulverization is carried out in order to enhance the dispersibility of MgO or its compound, hydrate, silica composite oxide and iron oxide, and further enhance the sinterability. It is more preferable that the subsequent particle size be 1 μm or less. Therefore, the crushing time is not particularly limited as long as the particle size of 1 μm or less can be obtained.

Although the firing temperature depends on the iron oxide content and the MgO / SiO ₂ molar ratio, it is within a range such that the porosity of the sintered body obtained by the Archimedes method can be as low as 0.5% or less. Good, MgO / SiO ₂ molar ratio 3
In the above cases, 1530 to 1650 ° C is a more preferable range. The firing atmosphere is not limited to the air atmosphere, but may be a non-oxidizing atmosphere or a reducing atmosphere.

As described above, when the semiconductive ceramics of the present invention are used, in addition to the characteristic that the static electricity charged can be quickly released, the processing accuracy such as bending strength, Young's modulus, hardness and fracture toughness is affected. The mechanical properties of the sintered body can be improved.

Further, for example, in a magnetic recording device or a jig such as a handling jig or tweezers used in the manufacturing process or mounting process of various electronic components, at least the contact surface with various components is the semiconductive ceramic of the present invention. If it is formed by, the static electricity can be removed and the adverse effect of magnetism can be prevented.

Further, spacers 12, shims 11 and clamps 13 for positioning and holding a plurality of magnetic disk substrates 16 incorporated in the magnetic recording apparatus shown in FIG. 1 at predetermined intervals are formed of the semiconductive ceramic of the present invention. For example, the static electricity charged on the magnetic disk substrate 16 can be quickly removed. Further, since the semiconductive ceramics of the present invention are excellent in bending strength, Young's modulus, hardness and fracture toughness, not only can the flatness of the contact surface with the magnetic disk substrate 16 be processed with high accuracy of 3 μm or less, It is also possible to obtain highly precise processing, for example, the flatness of a highly precise region of 1 μm or less, so that the magnetic disk substrate 1
The disc is not shaken or distorted when tightening or rotating at high speed. Therefore, if the magnetic disk substrate holding member is formed of the semiconductive ceramic of the present invention, stable writing and reading of information can be always realized, and a magnetic recording device capable of high density recording can be easily manufactured. be able to.

Further, the semiconductive ceramics of the present invention can be suitably used as a guide member for guiding the running of a magnetic tape, a static electricity removing member such as an electrodeposition coating nozzle used for coating automobiles, etc. It can also be used as a ceramic sensor, a ceramic heater, or a probe for evaluating resistance in semiconductor / thin film processes.

[0037]

EXAMPLE Here, a semiconductive ceramic of the present invention and a conventional semiconductive ceramic containing forsterite as a main component were prepared, and the volume resistivity, bending strength, Young's modulus,
An experiment was conducted to compare hardness, fracture toughness and coefficient of thermal expansion.

Commercially available MgO, silica composite oxide (talc (Mg ₃ Si ₄ O ₁₀ (OH) ₂ )), and iron oxide (Fe ₂ O ₃ ) were prepared as starting materials. As shown in Table 1, MgO and silica composite oxide are MgO / SiO ₂
Were blended so that the molar ratio thereof was 2, 3 or 4. The amount of iron oxide added was 25 or 30% by weight for those having a MgO / SiO ₂ molar ratio of 2 (conventional 1 and conventional 2), and for those having a MgO / SiO ₂ molar ratio of 3 or 4 (Sample No. 1 to No. 1). For 12), 10, 15, 20, 25,
Formulation was carried out so as to be 30 or 40% by weight, respectively.

The above-prepared raw material powders, water and dispersant were put into a predetermined container containing alumina balls having a diameter of 5-10 mm, and the container was rotated at a predetermined speed for 12 hours,
After crushing and mixing to reduce the particle size to 1 μm or less, the obtained slurry is recovered, polyvinyl alcohol and polyethylene glycol are added as a binder to this, and the mixture is stirred and then granulated by a spray granulator (spray dryer). went. Then, the granulated powder is molded into a predetermined shape, and 1
Firing was performed at a temperature between 500 and 1700 ° C. to obtain sintered bodies each having a porosity value of 0.5% or less measured by the Archimedes method. Tables 1 and 2 show the results of X-ray diffraction analysis of each of the obtained sintered bodies and the measurement results of volume resistivity, bending strength, Young's modulus, hardness, fracture toughness, and thermal expansion coefficient. Here, the “X-ray diffraction peak intensity ratio” in Table 1 means the above-mentioned peak intensity ratio, that is, MgFe ₂ when the MgO peak intensity in the vicinity of 2θ = 43 ° of the MgO crystal phase in X-ray diffraction is 1. O ₄ , Fe ₃ O ₄ , Fe ₂
It means the peak intensity around 2θ = 35 to 36 ° in which a crystal phase such as O ₃ is mixed. In addition, about the sample in which "-" is written in Table 1, it shows that MgO was not detected.

The above analysis and each measurement were carried out as follows. <Analysis by X-ray diffraction> Analysis was performed using an analyzer RINT manufactured by Rigaku. <Volume resistivity> The specific resistance was measured according to JIS C 2141. <Bending strength> The bending strength was measured according to JIS R 1601. <Young's modulus> The measurement was performed according to JIS R 1602. <Hardness> The hardness was measured according to JIS R 1610. <Fracture toughness> The fracture toughness was measured according to JIS R 1607. <Thermal expansion coefficient> The thermal expansion coefficient was measured according to JIS R 1618.

[0041]

[Table 1]

[Table 2]

From Tables 1 and 2, sample Nos. Included in the scope of the present invention. 1 to 12 are bending strengths as compared with Conventional 1 and Conventional 2 in which the MgO crystal phase is not detected by X-ray diffraction,
The Young's modulus, hardness and fracture toughness were high. As an example of the X-ray diffraction result, Sample No. 3 and No. Each crystal peak of 9 is shown in FIG. 2 and FIG.

Further, as a result of polishing the sintered body produced by the above method with a diamond wheel, sample N
o. For 1 to 12, flatness of 3 μm or less was obtained. The flatness was measured according to JIS B 0621.

From the above test results, 2MgO.SiO ₂
Bending strength and Young's modulus are obtained by newly depositing MgO crystals in a sintered body in a semiconductive ceramic having MgFe ₂ O ₄ , Fe ₂ O ₃ , and Fe ₃ O ₄ as a main crystal phase. It was confirmed that mechanical properties such as hardness, fracture toughness and the like were improved. From this, sample No. within the scope of the present invention.
It can be said that 1 to 12 are very excellent as magnetic disk substrate holding members and can be suitably used.

[0045]

According to the present invention, the mechanical properties that affect the workability of the sintered body are in a more preferable range, that is, the bending strength is 150 MPa or more, the Young's modulus is 200 GPa or more, the hardness is 8 GPa or more, and the fracture is caused. Toughness value is 1.5 MPa
m ^0.5 or more, and a volume resistivity of 10 ⁴ to 10 ⁷ Ω required as a holding member for a magnetic disk substrate.
It can be set to cm, and a desired coefficient of thermal expansion can be obtained. Further, there is an effect that it is possible to improve the durability by reducing the problem that chipping easily occurs even under various impacts.

Further, when the semiconductive ceramic of the present invention is used as a holding member for a magnetic disk substrate, the processing accuracy of the holding member for a magnetic disk substrate and the durability against impact can be further improved. Specifically, the flatness of the contact surface of the holding member with the magnetic disk substrate is set to 3 μm.
Since it can be processed with a high accuracy of m or less, the flatness of the magnetic disk substrate to be held can be maintained with high accuracy even when the magnetic disk substrate is held at a high speed, and chipping is less likely to occur even when an impact is applied. Since it is possible to prevent the debris associated with hanging from biting into the magnetic disk substrate and the magnetic head,
There is an effect that it is possible to prevent an error from occurring when recording and reproducing data.

Further, in a magnetic recording device, jigs such as handling jigs and tweezers used in the manufacturing process and mounting process of various electronic components, at least the contact surface with various components is formed of the semiconductive ceramic of the present invention. By doing so, it is possible to remove static electricity and prevent the adverse effect of magnetism.

[Brief description of drawings]

FIG. 1 is a view showing a cross section of a magnetic recording device incorporating a holding member for a magnetic disk substrate.

FIG. 2 shows a sample No. shown in the embodiment of the present invention. FIG. 3 is a spectrum diagram showing crystal peaks in X-ray diffraction of Sample No. 3.

FIG. 3 shows a sample No. shown in an example of the present invention. 9 is a spectrum diagram showing crystal peaks in X-ray diffraction of Sample No. 9. FIG.

[Explanation of symbols]

10: Magnetic disk device 11: Sim 12: Spacer 13: Clamp 14: Rotation axis 15: Hub 16: Magnetic disk substrate 17: Screw 18: Magnetic head

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4G030 AA07 AA27 AA37 BA02 GA03                       GA04 GA05 GA09 GA14 GA15                       GA22 GA27 HA08                 5D138 UA03 UA11 UA26 UA29                 5G301 CA02 CA12 CA18 CA24 CA25                       CA28 CA30 CD10 CE02

Claims (6)

[Claims] 1. Sintering having 2MgO.SiO ₂ as a main crystal phase and at least one crystal selected from MgFe ₂ O ₄ , Fe ₃ O ₄ and Fe ₂ O ₃ and a crystal of MgO as a sub crystal phase. A semiconductive ceramic characterized by comprising a body. 2. When the peak intensity in the vicinity of 2θ = 43 ° of the MgO crystal phase obtained by analyzing the semiconductive ceramic by X-ray diffraction is 1, MgFe ₂ O ₄ , Fe
₃ crystal phase of O ₄ and Fe ₂ O ₃ are mixed 2 [Theta] = 35-36
The semiconductive ceramic according to claim 1, which has a peak intensity of around 0.2 to 4. 3. M contained in the semiconductive ceramics.
g is 40 to 68 wt% in terms of MgO, Si is 14.5 to 30 wt% in terms of SiO ₂ , and Fe is 10 in terms of Fe ₂ O _3.
The content of the semiconductive ceramic according to claim 1 is 2 to 40% by weight. 4. The volume resistivity of the semiconductive ceramic is 10 ⁴ to 10 ⁷ Ω · cm, the bending strength is 150 MPa or more, the Young's modulus is 200 GPa or more, the hardness is 8 GPa or more, and the fracture toughness value is 1.5 MPa · m. ^{It is 0.5} or more, The semiconductive ceramics in any one of Claims 1-3. 5. A holding member for holding a magnetic disk substrate at a predetermined position, which is made of the semiconductive ceramic according to any one of claims 1 to 4, and is a contact surface with the magnetic disk substrate. The magnetic disk substrate holding member is characterized by having a flatness of 3 μm or less. 6. A jig or tool formed of the semiconductive ceramic according to any one of claims 1 to 4.