JP7296795B2 - cordierite crystals - Google Patents
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Description
本発明は、コーディエライト質結晶に関する。 The present invention relates to cordierite crystals.
近年、熱膨張しにくいセラミックスが種々の分野で採用されている。このような低熱膨張性のセラミックスとしては、例えば、特許文献１に開示されているようなコーディエライト質セラミックスが注目されている。 In recent years, ceramics that are resistant to thermal expansion have been used in various fields. As such low thermal expansion ceramics, for example, cordierite ceramics as disclosed in Patent Document 1 have attracted attention.
本開示に係るコーディエライト質結晶は、コーディエライト結晶相を主結晶相とし、組成式をＭｇ8Ａｌ16Ｓｉ20(1-x)Ｔｉ20xＯ72と表したときに、ｘが０．１～０．３である。結晶系が斜方晶系で、斜方晶系におけるＴ１サイトのＳｉおよびＴ２サイトのＳｉそれぞれに、Ｔｉが同数または同程度の数となるように置換している。２７３Ｋ以上９００Ｋ以下において、Ｏ－Ａｌ－Ｏのなす角度の変化率が正の値を有し、Ｏ－Ｓｉ－Ｏのなす角度の変化率が負の値を有する。 The cordierite crystal according to the present disclosure has a cordierite crystal phase as a main crystal phase, and has a composition formula of Mg 8 Al 16 Si 20(1-x) Ti 20x O 72 , where x is 0.5. 1 to 0.3. The crystal system is an orthorhombic system, and the Si at the T1 site and the Si at the T2 site in the orthorhombic system are substituted with Ti in the same or approximately the same number. Between 273 K and 900 K, the rate of change of the angle formed by O--Al--O has a positive value and the rate of change of the angle formed by O--Si--O has a negative value.
従来使用されているコーディエライト質セラミックスは低熱膨張性を有しているものの、採用される分野によっては、熱膨張に関してさらに厳しい基準を求められる場合がある。 Cordierite ceramics, which have been conventionally used, have low thermal expansion, but depending on the field in which they are used, stricter standards for thermal expansion may be required.
本開示に係るコーディエライト質結晶は、上記のように、コーディエライト結晶相を主結晶相とする。組成式をＭｇ8Ａｌ16Ｓｉ20(1-x)Ｔｉ20xＯ72と表したときに、ｘが０．１～０．３である。結晶系が斜方晶系で、斜方晶系におけるＴ１サイトのＳｉおよびＴ２サイトのＳｉそれぞれに、Ｔｉが同数または同程度の数となるように置換している。Ｏ－Ａｌ－Ｏのなす角度の変化率は、２７３Ｋ以上９００Ｋ以下において正の値を有し、Ｏ－Ｓｉ－Ｏのなす角度の変化率は、２７３Ｋ以上９００Ｋ以下において負の値を有する。本開示に係るコーディエライト質結晶は、２７３Ｋ以上９００Ｋ以下において、Ｏ－Ａｌ－Ｏのなす角度の変化率が正の値を有することから、結晶軸ａおよび結晶軸ｂの格子定数の変化率が正の値を示す。本開示に係るコーディエライト質結晶は、２７３Ｋ以上９００Ｋ以下において、Ｏ－Ｓｉ－Ｏのなす角度の変化率が負の値を有することから、結晶軸ｃの格子定数の変化率が負の値を示す。さらに、結晶軸ａおよび結晶軸ｂの格子定数の変化率と結晶軸ｃの格子定数の変化率とが、略対称性を示す。そのため、本開示に係るコーディエライト質結晶は、熱膨張しにくい優れた低熱膨張性を有する。 The cordierite crystal according to the present disclosure has the cordierite crystal phase as the main crystal phase, as described above. When the compositional formula is expressed as Mg 8 Al 16 Si 20(1-x) Ti 20x O 72 , x is 0.1 to 0.3. The crystal system is an orthorhombic system, and the Si at the T1 site and the Si at the T2 site in the orthorhombic system are substituted with Ti in the same or approximately the same number. The rate of change of the angle formed by O--Al--O has a positive value at 273K or more and 900K or less, and the rate of change of the angle formed by O--Si--O has a negative value at 273K or more and 900K or less. In the cordierite crystal according to the present disclosure, the rate of change of the angle formed by O—Al—O has a positive value at 273 K or more and 900 K or less. indicates a positive value. In the cordierite crystal according to the present disclosure, the rate of change of the angle formed by O—Si—O has a negative value at 273 K or more and 900 K or less, so the rate of change of the lattice constant of the crystal axis c has a negative value. indicates Furthermore, the rate of change of the lattice constants of the crystal axis a and the crystal axis b and the rate of change of the lattice constant of the crystal axis c exhibit substantially symmetry. Therefore, the cordierite crystals according to the present disclosure have excellent low thermal expansion properties that are resistant to thermal expansion.
本開示の一実施形態に係るコーディエライト質結晶は、コーディエライト結晶相を主結晶相とし、組成式をＭｇ8Ａｌ16Ｓｉ20(1-x)Ｔｉ20xＯ72と表したときに、ｘが０．１～０．３である。本明細書において「コーディエライト結晶相を主結晶相とする」とは、コーディエライト質結晶中にコーディエライトの基本的な成分が８０質量％以上含まれていることを意味する。本明細書において「コーディエライトの基本的な成分」とは、Ｍｇ、ＡｌおよびＳｉを意味する。これらの元素をそれぞれ酸化物として表したときに、ＭｇＯ、Ａｌ2Ｏ3およびＳｉＯ2の各金属酸化物の合計量が全量の８０質量％以上であればよい。 A cordierite crystal according to an embodiment of the present disclosure has a cordierite crystal phase as a main crystal phase, and when the composition formula is expressed as Mg 8 Al 16 Si 20(1-x) Ti 20x O 72 , x is 0.1 to 0.3. In the present specification, "having a cordierite crystal phase as the main crystal phase" means that cordierite crystals contain 80% by mass or more of the basic components of cordierite. As used herein, "basic components of cordierite" means Mg, Al and Si. When these elements are expressed as oxides, the total amount of each metal oxide of MgO, Al2O3 and SiO2 should be 80% by mass or more of the total amount.
まず、コーディエライトには、結晶の単位格子に２０個のＳｉが存在している。一実施形態に係るコーディエライト質結晶は斜方晶系を有しており、組成式Ｍｇ8Ａｌ16Ｓｉ20(1-x)Ｔｉ20xＯ72（ｘ＝０．１～０．３）から、２０個のＳｉのうち２～６個のＳｉがＴｉに置換されている。置換されるＳｉは任意ではなく、Ｔ１サイトのＳｉおよびＴ２サイトのＳｉそれぞれに、Ｔｉが同数または同程度の数となるように置換されている。本明細書において「同程度の数」とは、Ｔ２サイトのＴｉ数とＴ１サイトのＴｉ数の比が１：０．７～１：１．３の範囲内になること（Ｔ１サイトのＴｉ数またはＴ２サイトのＴｉ数のいずれかを規定値１としたときに３０％以内）を意味する。Ｔ１サイトのＳｉおよびＴ２サイトのＳｉについては、図１に示す。図１には、ｘが０．２の場合を示しており、Ｔ１サイトのＳｉのうちの２個およびＴ２サイトのＳｉのうちの２個がＴｉで置換されている。 First, cordierite has 20 Si atoms in the unit cell of the crystal. The cordierite crystal according to one embodiment has an orthorhombic system, and the composition formula Mg 8 Al 16 Si 20(1-x) Ti 20x O 72 (x=0.1 to 0.3) , 2 to 6 Si out of 20 Si are substituted with Ti. The Si to be substituted is not arbitrary, and the Si at the T1 site and the Si at the T2 site are substituted with Ti in the same number or the same number. As used herein, the term “similar number” means that the ratio of the number of Ti at the T2 site to the number of Ti at the T1 site is within the range of 1:0.7 to 1:1.3 (the number of Ti at the T1 site or within 30% when either of the Ti numbers at the T2 site is set to a specified value of 1). Si at the T1 site and Si at the T2 site are shown in FIG. FIG. 1 shows the case where x is 0.2, and two of the Si at the T1 site and two of the Si at the T2 site are replaced with Ti.
ＳｉをＴｉで置換しない場合や、Ｔｉで置換したとしても、例えばＴ１サイトのＳｉのみを置換したりなど上述した以外の置換であれば、優れた低熱膨張性が発揮されない。Ｔ１サイトのＳｉおよびＴ２サイトのＳｉそれぞれに、Ｔｉが同数または同程度の数となるように置換されることによって、Ｓｉ（およびＴｉ）原子で構成される６員環の回転が促進される。その結果、優れた低熱膨張性が発揮される。上記の組成式においてｘが０．２の場合に、得られるコーディエライト質結晶は、より優れた低熱膨張性を発揮する。 If Si is not replaced with Ti, or even if it is replaced with Ti, if the replacement is other than the above, such as replacing only Si at the T1 site, excellent low thermal expansion properties cannot be exhibited. The rotation of the six-membered ring composed of Si (and Ti) atoms is promoted by substituting Ti at the same or similar number for each of Si at the T1 site and Si at the T2 site. As a result, excellent low thermal expansion is exhibited. When x is 0.2 in the above compositional formula, the obtained cordierite crystal exhibits a more excellent low thermal expansion property.
ＳｉにおいてＴ１サイトおよびＴ２サイトは、結晶の対称性で区別され、Ｓｉ－Ｏの結合角度や金属原子の配置によって区別している。具体的には、コーディエライトは、Ｓｉを中心としてＯで囲まれた四面体が結晶軸ａおよび結晶軸ｂ方向に連結して６員環を構成している。その中で、Ｍｇを囲むように配置されている四面体の中心に位置するＳｉは「Ｔ１サイト」と定義され、その他のＳｉは「Ｔ２サイト」と定義される。 The T1 site and the T2 site in Si are distinguished by crystal symmetry, and are distinguished by the Si—O bond angle and arrangement of metal atoms. Specifically, cordierite forms a six-membered ring in which tetrahedrons surrounded by O with Si at the center are connected in the directions of crystal axis a and crystal axis b. Among them, Si positioned at the center of the tetrahedron surrounding Mg is defined as "T1 site", and other Si is defined as "T2 site".
一実施形態に係るコーディエライト質結晶は、２７３Ｋ以上９００Ｋ以下において、Ｏ－Ａｌ－Ｏのなす角度の変化率が正の値を有し、Ｏ－Ｓｉ－Ｏのなす角度の変化率が負の値を有する。具体的には、図２に基づいて説明する。 The cordierite crystal according to one embodiment has a positive rate of change in the angle formed by O—Al—O and a negative rate of change in the angle formed by O—Si—O at 273 K or more and 900 K or less. has a value of Specifically, it will be described based on FIG.
図２は、本開示の一実施形態に係るコーディエライト質結晶について、２７３Ｋ以上９００Ｋ以下におけるＯ－Ａｌ－Ｏのなす角度の変化率、およびＯ－Ｓｉ－Ｏのなす角度の変化率を示したグラフである。図２に示すように、Ｏ－Ａｌ－Ｏのなす角度の変化率は、２７３Ｋ以上９００Ｋ以下において正の値を有している。一方、Ｏ－Ｓｉ－Ｏのなす角度の変化率は、２７３Ｋから９００Ｋまでにおいて負の値を有している。 FIG. 2 shows the rate of change in the angle formed by O--Al--O and the rate of change in the angle formed by O--Si--O at 273 K or more and 900 K or less for a cordierite crystal according to an embodiment of the present disclosure. is a graph. As shown in FIG. 2, the change rate of the angle formed by O--Al--O has a positive value at 273K or more and 900K or less. On the other hand, the rate of change of the angle formed by O--Si--O has a negative value from 273K to 900K.
Ｏ－Ａｌ－Ｏのなす角度の変化率が正の値を有し、Ｏ－Ｓｉ－Ｏのなす角度の変化率が負の値を有することによって、結晶軸ａおよび結晶軸ｂ方向に連結した６員環が回転して、結晶軸ｃ方向に収縮する。その結果、一実施形態に係るコーディエライト質結晶は、優れた低熱膨張性が発揮される。Ｏ－Ａｌ－Ｏのなす角度の変化率が正の値を有し、Ｏ－Ｓｉ－Ｏのなす角度の変化率が負の値を有していれば、変化率は限定されない。例えば、Ｏ－Ａｌ－Ｏのなす角度の変化率およびＯ－Ｓｉ－Ｏのなす角度の変化率が、２７３Ｋの値を基準として、９００Ｋ以下の温度範囲において絶対値で０．７％以下であってもよい。 The rate of change of the angle formed by O—Al—O has a positive value and the rate of change of the angle formed by O—Si—O has a negative value, so that the crystal axis a and the crystal axis b are connected. The 6-membered ring rotates and contracts in the crystal axis c direction. As a result, the cordierite crystal according to one embodiment exhibits excellent low thermal expansion properties. The rate of change of the angle formed by O--Al--O is not limited as long as the rate of change of the angle formed by O--Al--O has a positive value and the rate of change of the angle formed by O--Si--O has a negative value. For example, the rate of change of the angle formed by O--Al--O and the rate of change of the angle formed by O--Si--O are 0.7% or less in absolute value in the temperature range of 900 K or less with respect to the value of 273 K. may
さらに、Ｏ－Ａｌ－Ｏのなす角度の変化率およびＯ－Ｓｉ－Ｏのなす角度の変化率が、２７３Ｋの値を基準として、５５０Ｋ以上９００Ｋ以下の温度範囲において絶対値で０．１％以上０．７％以下であってもよい。 Furthermore, the rate of change of the angle formed by O—Al—O and the rate of change of the angle formed by O—Si—O are 0.1% or more in absolute value in the temperature range of 550 K or more and 900 K or less based on the value of 273 K. It may be 0.7% or less.
本開示の一実施形態に係るコーディエライト質結晶は、２７３Ｋ以上９００Ｋ以下において、Ｏ－Ａｌ－Ｏのなす角度の変化率が正の値を有することから、図３に示すように、結晶軸ａおよび結晶軸ｂの格子定数の変化率が正の値を有し、Ｏ－Ｓｉ－Ｏのなす角度の変化率が負の値を有することから、図３に示すように、結晶軸ｃの格子定数の変化率が負の値を有する。さらに、図３に示すように、結晶軸ａおよび結晶軸ｂの格子定数の変化率と結晶軸ｃの格子定数の変化率とが、略対称性を示す。 In the cordierite crystal according to an embodiment of the present disclosure, the rate of change of the angle formed by O—Al—O has a positive value at 273 K or higher and 900 K or lower. Since the rate of change of the lattice constant of a and the crystal axis b has a positive value, and the rate of change of the angle formed by O—Si—O has a negative value, as shown in FIG. The rate of change of lattice constant has a negative value. Furthermore, as shown in FIG. 3, the rate of change of the lattice constants of the crystal axis a and the crystal axis b and the rate of change of the lattice constant of the crystal axis c exhibit substantially symmetry.
図３に示すように、例えば４８０Ｋ付近において、結晶軸ａおよび結晶軸ｂの格子定数の変化率が＋０．２～＋０．３％程度、結晶軸ｃの格子定数の変化率が－０．２～－０．３％程度と、略対象となり、６８０Ｋ付近においても結晶軸ａおよび結晶軸ｂの格子定数の変化率が＋１．１～＋１．２％程度、結晶軸ｃの格子定数の変化率が－１．１～－１．２％程度と、略対象となっている。このように、ある温度において結晶軸ａおよび結晶軸ｂの格子定数の変化率が＋ａ％程度であり、結晶軸ｃの格子定数の変化率が－ａ％程度である場合、結晶軸ａおよび結晶軸ｂの格子定数の変化率と結晶軸ｃの格子定数の変化率とが、略対称性を示すといえる。そのため、本開示の一実施形態に係るコーディエライト質結晶は、熱膨張しにくい優れた低熱膨張性を有する。 As shown in FIG. 3, for example, at around 480 K, the rate of change of the lattice constants of the crystal axis a and the crystal axis b is about +0.2 to +0.3%, and the rate of change of the lattice constant of the crystal axis c is -0.2%. ~ -0.3%, which is almost the same, and even at around 680K, the change rate of the lattice constants of the crystal axis a and the crystal axis b is about +1.1 to +1.2%, and the change rate of the lattice constant of the crystal axis c. is about -1.1% to -1.2%, which is roughly the target. Thus, when the rate of change of the lattice constant of the crystal axis a and the crystal axis b is about +a% at a certain temperature and the rate of change of the lattice constant of the crystal axis c is about −a%, the crystal axis a and the crystal It can be said that the rate of change of the lattice constant of the axis b and the rate of change of the lattice constant of the crystal axis c exhibit substantially symmetry. Therefore, the cordierite crystal according to one embodiment of the present disclosure has an excellent low thermal expansion property that is resistant to thermal expansion.
一方、Ｔｉで置換していないコーディエライト結晶は、結晶軸ａおよび結晶軸ｂの格子定数の変化率と結晶軸ｃの格子定数の変化率とが非対称となる。そのため、このようなコーディエライト結晶は、低熱膨張性に乏しくなる。 On the other hand, in cordierite crystals not substituted with Ti, the rate of change of the lattice constants of the crystal axes a and b is asymmetric with the rate of change of the lattice constant of the crystal axis c. Therefore, such cordierite crystals are poor in low thermal expansion properties.
さらに、Ｔｉで置換したとしても、Ｔ１サイトのＳｉおよびＴ２サイトのＳｉにおいて同数または同程度の数となるようにＴｉで置換されていなければ、結晶軸ａおよび結晶軸ｂの格子定数の変化率と結晶軸ｃの格子定数の変化率とが非対称となる。そのため、このようなコーディエライト質結晶も、低熱膨張性に乏しくなる。 Furthermore, even if Ti is substituted, the rate of change in the lattice constants of the crystal axis a and the crystal axis b will and the change rate of the lattice constant of the crystal axis c are asymmetric. Therefore, such cordierite crystals also have poor low thermal expansion properties.
図４は、Ｔ１サイトのＳｉのみをＴｉで置換した場合のコーディエライト質結晶の２７３Ｋ以上９００Ｋ以下における格子定数の変化率を示すグラフである。図４に示すように、Ｔ１サイトのＳｉおよびＴ２サイトのＳｉにおいて、同数または同程度の数となるようにＴｉで置換されていなければ、結晶軸ａおよび結晶軸ｂの格子定数の変化率と結晶軸ｃの格子定数の変化率とが非対称となることがわかる。このような挙動を示すコーディエライト質結晶は、低熱膨張性に乏しくなる。 FIG. 4 is a graph showing the rate of change in lattice constant at 273K or more and 900K or less of cordierite crystals when only Si at the T1 site is replaced with Ti. As shown in FIG. 4, if the Si at the T1 site and the Si at the T2 site are not substituted with Ti in the same or similar numbers, the change rate of the lattice constants of the crystal axis a and the crystal axis b and It can be seen that the change rate of the lattice constant of the crystal axis c is asymmetrical. Cordierite crystals exhibiting such behavior are poor in low thermal expansion properties.
本開示に係るコーディエライト質結晶の物性については、量子力学のシュレディンガー方程式に則って、物質の中の電子の運動をコンピュータの力を借りて計算し検証した（第一原理計算）。コーディエライトには、上記のように結晶の単位格子に２０個のＳｉが存在している。この２０個のＳｉのうち、４個のＳｉをＴｉに置換してコーディエライト質結晶を得る場合、置換場所の組み合わせとしては４８４５通り（２０Ｃ４）存在する。これらの中で、空間群を用いて等しい対称性を有する構造を除外することで９８０通りに絞り込んだ。 The physical properties of the cordierite crystal according to the present disclosure were verified by calculating the motion of electrons in the material with the help of a computer according to the Schrödinger equation of quantum mechanics (first-principles calculation). In cordierite, 20 Si atoms exist in the crystal unit cell as described above. When 4 of the 20 Si are replaced with Ti to obtain a cordierite crystal, there are 4845 combinations (20C4) of replacement sites. Among these, 980 were narrowed down by excluding structures with equal symmetry using space groups.
９８０通り全ての構造についてエネルギー最適化を行い、平衡位置のｃ軸格子定数とポテンシャルエネルギーとを計算した。次いで、ｃ軸格子定数とエネルギーの分布とを用いて、計算結果を９種類の結晶構造グループに分けた。それぞれのグループからポテンシャルエネルギーが最も低い結晶構造を選別して分子動力学計算を実行した。 Energy optimization was performed for all 980 structures, and the c-axis lattice constant and potential energy of the equilibrium position were calculated. Then, using the c-axis lattice constant and energy distribution, the calculated results were divided into nine crystal structure groups. A crystal structure with the lowest potential energy was selected from each group and a molecular dynamics calculation was performed.
計算は、第一原理計算ソフト「ＳＩＥＳＴＡ」を使って実行した。計算条件は、ＰＢＥ汎関数およびノルム保存型基底関数を利用し、エネルギーカットオフを２５０Ｒｙｋ空間２×２×１とした。ＮＰＴ計算（Nose-Parrinello-Rahman thermostat）を用い、速度ベルレ法を用いて時間に関する数値積分を用いて１０ピコセカンド計算した。計算中は圧力を１気圧とし、温度を一定に設定した。設定温度は、２７３Ｋ、３７３Ｋ、４７３Ｋ、５７３Ｋ、６７３Ｋ、７７３Ｋおよび８７３Ｋとした。 The calculation was performed using first-principles calculation software "SIESTA". The calculation conditions used PBE functionals and norm-preserving basis functions, and set the energy cutoff to 250 Ryk space 2×2×1. NPT calculations (Nose-Parrinello-Rahman thermostat) were used to calculate 10 picoseconds using numerical integration over time using the Velocity Bell Level method. During the calculation, the pressure was set to 1 atm and the temperature was set constant. The set temperatures were 273K, 373K, 473K, 573K, 673K, 773K and 873K.
次いで、それぞれの分子動力学計算結果から結晶構造の時間変化を抽出した。結晶構造の時間変化から、全ての原子間結合の組み合わせ（Ｓｉ－Ｏ、Ｔｉ－ＯおよびＡｌ－Ｏ）について結合長を計算し、各温度（２７３Ｋ、３７３Ｋ、４７３Ｋ、５７３Ｋ、６７３Ｋ、７７３Ｋおよび８７３Ｋ）における平均値を求めた。 Next, the time change of the crystal structure was extracted from each molecular dynamics calculation result. From the time change of the crystal structure, the bond length was calculated for all combinations of interatomic bonds (Si—O, Ti—O and Al—O), and ) was calculated as the average value.
同様に、結晶構造の時間変化から全ての原子間角度の組み合わせ（Ｏ－Ｓｉ－Ｏ、Ｏ－Ｔｉ－ＯおよびＯ－Ａｌ－Ｏ）について結合角度を計算し、各温度（２７３Ｋ、３７３Ｋ、４７３Ｋ、５７３Ｋ、６７３Ｋ、７７３Ｋおよび８７３Ｋ）における平均値を求めた。 Similarly, bond angles were calculated for all combinations of interatomic angles (O-Si-O, O-Ti-O and O-Al-O) from the time change of the crystal structure, and each temperature (273K, 373K, 473K , 573K, 673K, 773K and 873K) were determined.
第一原理計算は数値積分を行うため、計算誤差を生じる。計算誤差を可能な限り少なくするために、下記の式（Ｉ）を用いて計算結果の補正を行った。式（Ｉ）中、Ｘ（Ｔ）は上述の計算によって求めた結合長および結合角度を示し、Ｔは、２７３Ｋ、３７３Ｋ、４７３Ｋ、５７３Ｋ、６７３Ｋ、７７３Ｋおよび８７３Ｋの各温度を示す。
Ｘ’（Ｔ）＝｛Ｘ（Ｔ－１）＋Ｘ（Ｔ）＋Ｘ（Ｔ＋１）｝／３ （Ｉ）
Since the first-principles calculation involves numerical integration, calculation errors occur. In order to reduce calculation errors as much as possible, the calculation results were corrected using the following formula (I). In formula (I), X(T) indicates the bond length and bond angle obtained by the above calculation, and T indicates each temperature of 273K, 373K, 473K, 573K, 673K, 773K and 873K.
X′(T)={X(T−1)+X(T)+X(T+1)}/3 (I)
この式（Ｉ）を用いることで、計算精度がより向上する。このようにして得られた全ての計算結果から、熱膨張係数が小さい場合の結晶構造を特定した。 By using this formula (I), calculation accuracy is further improved. From all the calculation results obtained in this manner, a crystal structure with a small coefficient of thermal expansion was specified.
Claims (3)
結晶系が斜方晶系で、斜方晶系におけるＴ１サイトのＳｉおよびＴ２サイトのＳｉそれぞれに、Ｔｉが置換しており、
該Ｔｉは、Ｔ２サイトのＴｉ数とＴ１サイトのＴｉ数との比が１：０．７～１：１．３の範囲であり、
２７３Ｋの値を基準とした場合、２７３Ｋ以上９００Ｋ以下において、Ｏ－Ａｌ－Ｏのなす角度の変化率が正の値を有し、Ｏ－Ｓｉ－Ｏのなす角度の変化率が負の値を有する、
コーディエライト質結晶。 When the cordierite crystal phase is the main crystal phase and the composition formula is expressed as Mg 8 Al 16 Si 20 (1-x) Ti 20x O 72 , x is 0.1 to 0.3,
The crystal system is an orthorhombic system, and Ti is substituted for Si at the T1 site and Si at the T2 site in the orthorhombic system,
The Ti has a ratio of the Ti number at the T2 site to the Ti number at the T1 site in the range of 1:0.7 to 1:1.3,
When the value of 273K is used as a reference, the rate of change of the angle formed by O—Al—O has a positive value and the rate of change of the angle formed by O—Si—O has a negative value at 273K or more and 900K or less. have
cordierite crystals.
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