# Patent

## Title
Mechanoluminescence material, producing method thereof, and usage thereof

## Abstract

A mechanoluminescence material comprising a mother body material and a luminescence center added to the mother body material. The mother body material is constituted of at least one kind of oxide selected from alumino silicate, aluminate, silicate, tantalate, niobate, gallium oxide, and ZrO2, and the luminescence center is at least one kind selected from a rare earth metal and a transition metal which emits light when electrons excited by mechanical energy are restored to a normal state.

## Background
FIELD OF THE INVENTION
The present invention relates to a so-called mechanoluminescence material that emits light by receiving mechanical force from outside, a producing method thereof, and usage thereof.
BACKGROUND OF THE INVENTION
Conventionally, it has been well known that: there is a material, emitting visible or substantially visible light at a low temperature such as a room temperature by receiving external stimulation, which functions as a so-called fluorescent phenomenon. Materials bringing about such a fluorescent phenomenon, namely fluorescent materials, are used in a panel light such as a fluorescent lamp and in a display such as a so-called Braun tube of CRT (Cathode Ray Tube).
It is typical that ultraviolet ray irradiation, electron ray irradiation, X-ray irradiation, radioactive ray irradiation, application of an electric field, chemical reaction, and the like are performed as external stimulation bringing about the fluorescent phenomenon, but a material that emits light by receiving mechanical force from outside is not well known.
The present inventors proposed the following two light-emitting materials. The one is a high intensity mechanoluminescence material (Japanese Unexamined Patent Publication No. 49251/2001 (Tokukai 2001-49251)(Publication date: Feb. 20, 2001)) made of (a) a material, constituted of at least one kind of aluminate having non-stoicheiometric composition, that includes lattice defect in which light is emitted when carriers excited by mechanical energy are restored to a normal state, or (b) a material whose mother body material includes at least one kind of a metal ion selected from a rare earth metal ion and a transition metal ion as a central ion of a luminescence center. The other is a light-emitting material (Japanese Unexamined Patent Publication No. 313878/2000 (Tokukai 2000-313878)(Publication date: Nov. 14, 2000)) whose mother body material is constituted of Y2SiO5, Ba3MgSi2O8, and BaSi2O5. However, these light-emitting materials are so insufficient in the luminous intensity that they cannot be put into practical usage. Thus, a material whose luminous intensity is higher has been required.
SUMMARY OF THE INVENTION
As a result of earnest study performed by the present inventors so as to develop a mechanoluminescence material having higher luminescence intensity, they found that: when a certain kind selected from alumino silicate, aluminate, silicate, tantalate, niobate, gallium oxide, and zirconium dioxide is used so as to produce a mother body material, it is possible to obtain a mechanoluminescence material whose luminescence intensity is high. As a result, they completed the present invention.
That is, the mechanoluminescence material of the present invention includes: a mother body material; and a luminescence center added to the mother body material, wherein:
said mother body material is constituted of at least one kind of oxide selected from:
alumino silicate having a structure indicated by a general formula (A)

xM1O.yAl2O3.zSiO2

(M1 in the formula is Ca, Ba or Sr, and a part thereof may be replaced with at least one kind selected from Na, K, and Mg, and each of x, y, and z is 1 or more);
aluminate having a structure indicated by a general formula (B)

xM3O.y Al2O3

(M3 in the formula is Ca or Ba, and a part thereof may be replaced with either Mg or La, and each of x and y is 1 or more);
silicate having a structure indicated by a general formula (C)

xM3O.ySiO2

(M3 in the formula is Ca or Sr, and a part thereof may be replaced with at least one kind selected from Na, Mg, Zn, Be, Mn, Zr, Ce, and Nb, and each of x and y is 1 or more), or indicated by Ba2 Mg SiO7;
tantalate or niobate having a structure indicated by a general formula (D)

xM4O.yM54O10

(M4 in the formula is Ca, Ba or Sr, and M5 is replaced with at least one kind selected from Ta and Nb, and each of x and y is 1 or more); and
gallium oxide having a structure indicated by a general formula (E)

xM6O.yGa2O3

(M6 in the formula is Ca, Ba or Sr, and a part thereof may be replaced with La, and each of x and y is 1 or more); and
said luminescence center is at least one kind selected from a rare earth metal and a transition metal which emits light when electrons excited by mechanical energy are restored to a normal state.
According to the arrangement, it is possible to obtain the mechanoluminescence material which functions as a novel high intensity mechanoluminescence material which emits light by receiving a mechanical force from outside such as a frictional force, a shearing force, an impulse force, a pressure, and a tensile force. Further, action of the mechanical force applied from outside can be directly converted into light so as to emit light, so that the mechanoluminescence material can be widely utilized as a completely novel optical element.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing how light is emitted according to stress in a case where mechanical force is applied to a sample in the form of pellet described in Example 1.
FIG. 2 is a graph showing how the luminescence intensity of the sample in the form of pellet described in Example 1 depends on stress.



DESCRIPTION OF THE EMBODIMENTS
One embodiment of the present invention is described as follows.
The mechanoluminescence material of the present invention is arranged so that a mother body material thereof includes a luminescence center. As the mother body material, an oxide selected from the aforementioned (A) through (E) groups and ZrO2 is used. Note that, in a case where parts of M1 to M3 and M6 shown in the aforementioned (A) through (C) and (E) groups are replaced with other elements described above, the replacement of the elements is performed so as to have a stoicheiometric composition corresponding to an atomic value thereof.
Examples of alumino silicate, belonging to the aforementioned (A) group, that functions as the mother body material, include:

    (Ca, Na)(Mg, Fe, Al, Ti)(Si, Al)2O6,
    (Ca, Na)2(Al, Mg, Fe)(Si, Ai)2O7,
    (Ca, Na2)Al2Si4O12,
    (K2, Ca, Mg, Na2)2Al4Si14O36,
    (K2, Sr, Mg, Na2)2Al4Si14O36,
    (Na, Ca)Al(Al, Si)2SiO8,
    (Na, Sr)Al(Al, Si)2SiO8,
    (Sr, K2, Na2)Al4Si14O36,
    (Sr, Na)(Mg, Fe, Al, Ti)(Si, Al)2O6,
    (Sr, Na)2(Al, Mg, Fe)(Si, Al)2O7,
    Ba2(Mg, Al)(Al, Si)SiO7,
    Ba2Al2SiO7,
    BaAl2Si2O8,
    BaNaAlSi2O7,
    Ca2(Mg, Al)(Al, Si)SiO7,
    CaAl2SiO8,
    CaNa2Al4Si4O16,
    Sr2(Mg, Al)(Al, Si)SiO7,
    Sr2Al2SiO7,
    SrNa2Al4Si4O6, and the like.


The elements in parentheses can be partially or entirely replaced with each other. That is, as to the elements in parentheses of the aforementioned chemical formula, any one of the elements in parentheses may be used, or two or more elements may be used at an arbitrary rate.
Note that, the alumino silicate may further include elements that are not included in a general formula xM1O.yAl2O3.zSiO2 shown as the mother body material belonging to the aforementioned (A) group. That is, as shown by the foregoing chemical formula, the alumino silicate may include Fe, Ti, and the like as oxide.
Further, examples of aluminate that functions as the mother body material belonging to the aforementioned (B) group include:

    BaAl8O13,
    BaMgAl6O11,
    CaLaAl3O7,
    CaMgAl6O11, and the like.


Further, examples of silicate which functions as the mother body material belonging to the aforementioned (C) group include:

    Ba(Zn, Mn, Fe, Mg)Si2O6,
    Ba2(Mg, Fe)Si2O7,
    Ba2BeSi2O7,
    Ba2MgSi2O7,
    Ca2BeSi2O7,
    CaMgSi2O6,
    CaMnSi2O6,
    CaZrSi2O,
    Sr(Zn, Mn, Fe, Mg)Si2O6,
    Sr2(Mg, Fe)Si2O7,
    Sr2B2SiO7,
    Sr2BeSi2O7,
    Sr2MgSi2O7,
    Sr2Na4CeFeNb2Si8O28,
    Sr3Si2O7,
    SrFeSi2O6,
    SrMgSi2O6, and the like. Note that, as to the elements in parentheses, the replacement can be performed as described above. Further, the silicate may further include elements that are not included in a general formula xM3O.ySiO2 shown as the mother body material belonging to the aforementioned (C) group. That is, as shown by the foregoing chemical formula, the silicate may include B, Fe, Ti, and the like as oxide.


Further, examples of tantalate or niobate which functions as the mother body material belonging to the aforementioned (D) group include:

    Sr(Ta, Nb)4O11.

Further, examples of the aforementioned (E) group include:

    SrGa12O19, and
    SrLaGa3O7.


In a case where the mother body materials are used as the mechanoluminescence material, it is possible to obtain particularly high luminescence intensity by using (Ca, Na)2(Al, Mg, Fe)(Si, Al)2O7, Ba2Al2SiO7, Ba2MgSi2O7, BaAl2Si2O8, BaAl8O13, Ca2(Mg, Al)(Al, Si)SiO7, Sr(Ta, Nb)4O11, Sr(Zn, Mn, Fe, Mg)Si2O6, Sr2(Mg, Al)(Al, Si)SiO7, Sr2Al2SiO7, Sr2MgSi2O7, Sr2Na4CeFeNb2Si8O28, SrMgSi2O6, and ZrO2.
Note that, the mother body materials belong to a crystal group indicated by the following point group in terms of a crystal structure.
1, {overscore (1)}, 2, 2/m, 6/m, m3m, {overscore (4)}2m, 622
The luminescence center added to the mother body material emits light when electrons excited by mechanical energy are restored to a normal state, and is constituted by combining (a) one kind or two or more kinds selected from the rare earth metal group with (b) one kind or two or more kinds selected from the transition metal group. The luminescence center is added to the mother body material, so that it is possible to obtain the mechanoluminescence material whose luminescence intensity is extremely improved. In this manner, the rare earth metal group and the transition metal group are used to extremely improve the luminescence intensity of the mechanoluminescence material, so that it is preferable to use the rare earth metal group and the transition metal group whose first energy of ionization is not more than 8 eV, particularly not more than 6 eV.
Concretely, the rare earth metal group and the transition metal group have unstable electron shells of 3d, 4d, 5d, or 4f. That is, examples of the rare earth metal include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and the like. Further, examples of the transition metal include Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, W, and the like.
Preferable transition metals of the foregoing transition metal group having an unstable 3d electron shell are Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and the like. Further, preferable transition metals of the foregoing transition metal group having an unstable 4d electron shell are Nb and Mo. Preferable transition metals of the foregoing transition metal group having an unstable 5d electron shell are Ta and W. Meanwhile, preferable rare earth metals of the foregoing rare earth metal group having an unstable 4f electron shell are Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, and the like.
A certain metal is selected from the rare earth metal group and the transition metal group as a preferable luminescence center, and which metal is preferable is determined depending on which mother body material is to be used. That is, the luminescence intensity and the most preferable luminescence center of the obtained mechanoluminescence material differ in accordance with combination of the mother body material and the luminescence center. Thus, it is preferable to select the luminescence center to be added in accordance with the mother body material to be used as required. Concretely, it is preferable to use Eu as the luminescence center in a case where Sr2Al2SiO7 or Sr2MgSi2O7 are used as the mother body material for example, and it is preferable to use Ti as the luminescence center in a case where ZrO2 is used as the mother body material.
Next, a producing method of the mechanoluminescence material of the present invention is described. The mechanoluminescence material of the present invention is produced by doping the rare earth metal and the transition metal each of which functions as the luminescence center on the aforementioned mother body material. Concretely, after mixing the mother body material and the rare earth metal and the transition metal each of which functions as the luminescence center, the resultant is sintered at a high temperature ranging from 600° C. to 1800° C. in a reduction atmosphere for at least 30 minutes, so that the mechanoluminescence material is obtained. If the sintering is performed after a flux such as boric acid has been added, the luminescence property of the obtained mechanoluminescence material is further improved.
Note that, it is possible to dope the rare earth metal and the transition metal on the mother body material by using the rare earth metal and the transition metal as simple substances, or by using a compound of the rare earth metal and a compound of the transition metal. Examples of the compound of the rare earth metal and the compound of the transition metal include: oxide, nitrate, and the like of the rare earth metal and the transition metal.
Further, an amount of the added rare earth metal and transition metal each of which functions as the luminescence center is set to be within 0.001 to 20 mass % with respect to the mother body material. This is based on the following reason: when the amount of the added luminescence center is less than 0.001 mass %, sufficient luminescence intensity cannot be obtained, and when the amount of the added luminescence center is more than 20 mass %, the crystal structure of the mother body material cannot be maintained, so that the luminescence efficiency declines. As a result, this is hard to use as the mechanoluminescence material.
The mechanoluminescence material of the present invention emits light when it receives a mechanical force applied from outside. Although the mechanical force is not particularly limited, examples of the mechanical force applied from outside include: a mechanical force such as a frictional force, a shearing force, an impulse force, a pressure, and a tensile force.
Although the luminescence intensity of the mechanoluminescence material depends on how the mechanical force which functions as an exciting source exerts influence, it is typical that: the more mechanical force is applied, the higher the luminescence intensity becomes. Thus, the luminescence intensity is measured, so that it is possible to know how much mechanical force is applied to the mechanoluminescence material. Thus, it is possible to detect, without touching the mechanoluminescence material, how much it is stressed, and it is also possible to visualize a condition under which it is stressed. Thus, the mechanoluminescence material is expected to be applied to a stress detector and other various fields.
Further, the mechanoluminescence material of the present invention is combined with other inorganic material or organic material except the mechanoluminescence material so as to constitute a composite material, and the mechanical force is applied from outside to the composite material, so that it is possible to cause the composite material to emit light. When, for example, the mechanoluminescence material is mixed with or put into an organic material such as resin and plastic at an arbitrary ratio so as to constitute the composite material, and the mechanical force is applied from outside to the composite material, the mechanoluminescence material is deformed so as to emit light. Alternately, glass and glass fiber may be used as the inorganic material in constituting the composite material so as to cause the mechanoluminescence material to emit light.
Alternately, a base material such as a heat-resisting base material may be used as other inorganic or organic material described above after providing the mechanoluminescence material thereon. That is, the mechanoluminescence material may be used as a coating film provided on a surface of the base material such as the heat-resisting base material. Note that, hereinbelow, the composite material, in which the mechanoluminescence material is used as the coating film provided on the surface of the heat-resisting base material, is referred to as a stacked material. When the mechanical force is applied from outside to the stacked material, the mechanoluminescence material layer provided on the surface of the base material is deformed so as to emit light. Thus, according to the stacked material of the present invention, it is possible to obtain light emission of a large area using a small quantity of the mechanoluminescence material.
In order to obtain the foregoing stacked material, a material compound that can constitute a predetermined mother body material is dissolved in dissolvent. Further, at least one kind of the luminescence center selected from the rare earth metal and the transition metal is added to the resultant so as to prepare an embrocation. Then, the embrocation is applied to the surface of the base material. Thereafter, the base material to which the embrocation has been applied is sintered, so that it is possible to form the stacked material in which the mechanoluminescence material is provided on the surface of the base material as the coating film.
Note that, examples of the material compound that can form the mother body material include: nitrate, halogenide, an alkoxy compound, and the like.
Further, it is preferable that the base material is the heat-resisting base material so as to sinter it upon providing the mechanoluminescence material on the surface thereof. Although the heat-resisting base material is not particularly limited, it is preferable to use the following materials for example: quartz; silicon; graphite; heat-resistance glass such as quartz glass and vycor glass; ceramics such as alumina, silicon nitride, silicon carbide, and molybdenum disilicide; a heat resisting steel such as a stainless steel; a heat resisting iron or a heat resisting alloy such as nickel, chromium, titanium, and molybdenum; cermet; cement; concrete; and the like.
Next, the present invention is further detailed based on the following Examples. However, the present invention is not necessarily limited to these Examples.
EXAMPLE 1
Sr2Al2SiO7 in the form of powder was used as the mother body material, and Eu2O3 which functioned as the luminescence center was added to the mother body material so that an amount of Eu2O3 was 0.05 mass % with respect to the mother body material. Further, boric acid which functioned as a flux was added to and mixed with the mother body material so that an amount of the boric acid was 10 mass % with respect to the resultant. The mixture was sintered at 1300° C. for four hours in an argon atmosphere containing 2.5 mass % hydrogen, so as to prepare a sintered compact of the mechanoluminescence material.
Next, the sintered compact that had been obtained was crushed into powder. 20 mass parts of the powder were put into 100 mass parts epoxy resin (trade name: Specifics-40, made by Struers Co., Ltd.) so as to prepare a sample in the form of pellet (hereinbelow, referred to as pellet sample).
A mechanical force of 1000N was applied, using a vise, to the pellet sample (Sr2Al2SiO7: Eu) obtained in the foregoing manner. FIG. 1 shows how the luminescence intensity brought about by the application of the mechanical force varies with time. Note that, the pellet sample emitted blue light so intensely that it could be perceived with an unaided eye.
Further, FIG. 2 is a graph showing how the luminescence intensity of the pellet sample (Sr2Al2SiO7: Eu) depends on the stress. According to the graph, it was found that: the luminescence intensity of the pellet sample depends on the stress, and the luminescence intensity increases as the load is applied more. Thus, it was found that: it is possible to evaluate the largeness of the applied stress by measuring the luminescence intensity.
EXAMPLE 2
The pellet samples of the mechanoluminescence material having the mother body material and the luminescence center shown in Table 1 was prepared in the same manner as in Example 1, and the luminescence intensity (cps) of each pellet sample was measured. Table 1 shows results of the measurement.









TABLE 1





SAMPLE

LUMINESCENCE


No.
COMPOSITION
INTENSITY (cps)

















1
Ca La Al3 O7: Ce
4912


2
Ca La Al3 O7: Eu
4376


3
Sr2 Al2 SiO7: Ce
28712


4
Sr2 Al2 SiO7: Eu
63116


5
Ba2 Al2 SiO7: Ce
321


6
Ba2 Al2 SiO7: Eu
43700


7
Sr2 Mg Si2O7: Eu
10000


8
Ba2 Mg Si2O7: Eu
10000









As shown in Table 1, it was found that particularly high luminescence intensity was brought about by the following pellet samples: the pellet samples (sample No. 3 to 4) in which Ce or Eu was doped on Sr2Al2SiO7, and the samples (sample No. 6 to 8) in which Eu was doped on each of Ba2Al2SiO7, Sr2MgSi2O7, and Ba2MgSi2O7.
EXAMPLE 3
The pellet samples of the mechanoluminescence material using the mother body material shown in Table 2 an using europium (Eu) as the luminescence center was prepared in the same manner as in Example 1, and the luminescence intensity (cps) of each pellet sample was measured. Table 2 shows results of the measurement.










TABLE 2








LUMINESCENCE



MOTHER BODY COMPOSITION
INTENSITY (cps)



















(Ca, Na)(Mg, Fe, Al, Ti)(Si, Al)2O6
874



(Ca, Na)2(Al, Mg, Fe)(Si, Al)2O7
12000



(Ca, Na2)Al2Si4O12
2490



(K2, Ca, Mg, Na2)2Al4Si14O36
256



(K2, Sr, Mg, Na2)2Al4Si14O36
237



(Na, Ca)Al(Al, Si)2SiO8
250



(Na, Sr)Al(Al, Si)2SiO8
1200



(Sr, K2, Na2)Al4Si14O36
211



(Sr, Na)(Mg, Fe, Al, Ti)(Si, Al)2O6
270



(Sr, Na)2(Al, Mg, Fe)(Si, Al)2O7
221



Ba2(Mg, Al)(Al, Si)SiO7
2356



BaAl2Si2O8
11600



BaNaAlSi2O7
120



Ca2(Mg, Al)(Al, Si)SiO7
10000



CaAl2SiO8
3116



CaNa2Al4Si4O16
126



Sr2(Mg, Al)(Al, Si)SiO7
28501



SrNa2Al4Si4O16
1564



BaAl8O13
31320



BaMgAl6O11
134



CaMgAl6O11
141



Ba(Zn, Mn, Fe, Mg)Si2O6
1256



Ba2(Mg, Fe)Si2O7
122



Ba2BeSi2O7
134



Ca2BeSi2O7
110



CaMgSi2O6
341



CaMnSi2O6
257



CaZrSi2O7
1426



Sr(Zn, Mn, Fe, Mg)Si2O6
77440



Sr2(Mg, Fe)Si2O7
6300



Sr2B2SiO7
1500



Sr2BeSi2O7
2851



Sr2MgSi2O7
10000



Sr2Na4CeFeNb2Si8O28
14500



Sr3Si2O7
158



SrFeSi2O6
411



SrMgSi2O6
21408



Sr(Ta, Nb)4O11
21408



SrGa12O19
128



SrLaGa3O7
788



ZrO2
16280










As shown in Table 2, it was found that particularly high luminescence intensity was brought about by the mechanoluminescence material in which Eu was doped on each of (Ca, Na)2(Al, Mg, Fe)(Si, Al)2O7, BaAl2Si2O8, Cs2(Mg, Al)(Al, Si)SiO7, Sr2(Mg, Al)(Al, Si)SiO7, BaAl8O13, Sr(Zn, Mn, Fe, Mg)Si2O6, Sr2MgSi2O7, Sr2Na4CeFeNb2Si8O28, SrMgSi2O6, and ZrO2.
The invention being thus described, it will be obvious that the same way may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

## Claims

1. A mechanoluminescence material, comprising: a mother body material; and a luminescence center added to the mother body material, wherein:
said mother body material is constituted of at least one kind of oxide selected from:
aluminate having a structure indicated by a general formula (B)


xM2O.yAl2O3


(M2 in the formula is Ca or Ba, and a part thereof may be replaced with either Mg or La, and each of x and y is 1 or more);
silicate having a structure indicated by a general formula (C)


Ba2MgSiO7;


tantalite or niobate having a structure indicated by a general formula (D)


xM4O.yM54O10


(M4 in the formula is Ca, Ba or Sr, and M5 is replaced with at least one kind selected from Ta and Nb, and each of x and y is 1 or more); and
gallium oxide having a structure indicated by a general formula (E)


xM6O.yGa2O3


(M6 in the formula is Ca, Ba or Sr, and a part thereof may be replaced with La, and each of x and y is 1 or more); and
said luminescence center is at least one kind selected from (i) a rare earth metal of at least one kind selected from Sc, Y, La, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and (ii) a transition metal of at least one kind selected from Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, and W.

2. The mechanoluminescence material as set forth in claim 1, wherein the rare earth metal and the transition metal are such that a first ionization energy is not more than 8 eV.

3. A mechanoluminescence material, comprising: a mother body material; and a luminescence center added to the mother body material, wherein:
said mother body material is alumino silicate having a structure indicated by a general formula


xM1O.yAl2O3.zSiO2


(M1 in the formula is Ca, Ba or Sr, and a part thereof may be replaced with at least one kind selected from Na, K, and Mg, and each of x, y, and z is 1 or more); and
said luminescence center is at least one kind selected from (i) a rare earth metal of at least one kind selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and (ii) a transition metal of at least one kind selected from Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, and W.

4. A mechanoluminescence material, comprising: a mother body material; and a luminescence center added to the mother body material, wherein:
said mother body material is silicate having a structure indicated by a general formula


xM3O.ySiO2


(M3 in the formula is Ca or Sr, and a part thereof may be replaced with at least one kind selected from Na, Mg, Zn, Be, Mn, Zr, Ce, and Nb, and each of x and y is 1 or more); and
said luminescence center is at least one kind selected from (i) a rare earth metal of at least one kind selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and (ii) a transition metal of at least one kind selected from Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, and W.