Electroceramics and Solid State Cheminstry Application of Lattice

電子セラミックスと固体化学 Electroceramics and Solid State Cheminstry 格子欠陥の利用 Application of Lattice Defects 学部　応用化学科　 片山　恵一

Today's subjects 電子セラミックスとは？ 固体化学とは？ What is Solid State Chemistry? 　　　　 Electroceramics? 　 これらの関係は？ What is the relationship between these two subjects ? 　 この関係は何に利用されている？ What has this relationship been utilized for? 　 The interdisciplinary study of these two subjects has developed technology, and has been producing lots of sophisticated products underpinned modern society.

講義の流れ Flow of today's talk • 電子セラミックスとは？ • What is Electroceramics? • 固体化学 • Solid State Chemistry • 実用例 • Application

電子セラミックスとは？ What is Electroceramics?

セラミックスとは？ What is a ceramic? 加熱して作製される非金属無機固体化合物 A ceramic is an inorganic, non-metallic solid prepared by heating. 　　　　　　　　例：陶磁器　pottery 　　　　　半導体材料として広範に利用されている。 　　　　　　In the 20 th century, new ceramic materials 　 　　　　　　 were developed for use in advanced ceramic 　　　　　　 engineering; for example, in semiconductors.

Definition of Ceramics セラミックスの定義 The term ‘ceramics’ is restricted to polycrystalline, inorganic, non-metallic materials that can acquire their mechanical strength through a firing or sintering process. Glass and single crystals are sometimes included as a matter of convenience. 　　　　　 厳密には多結晶を対象とするが、単結晶･ガラスを含む 場合もある

固体化学の基礎 Fundamental Solid State Chemistry

固体化学って何？ What is Solid State Chemistry? • • Preparative methods Crystal chemistry Phase diagrams Phase transition Electrical properties Magnetic properties Optical properties • • • Electroceramics Crystal defects Non-stoichiometry Solid solution

Crystal defects Point Defects § § Schottky defect Frenkel defect intrinsic and extrinsic defects Interchanged Atoms

Perfect and Imperfect Crystals • Perfect Crystals in which all atoms are at rest on their correct lattice positions. At all real temperatures, crystals are imperfect. • Imperfect Crystals which contain random defects, resulting in the deficiency of one element.

Stoichiometry and Non-stoichiometry • Stoichiometric compounds （化学量論組成化合物） • Non-stoichiometric compounds　　　　 （非化学量論組成化合物）

Example of Non-stoichiometric compounds Ferrous oxide: Fe. O（酸化鉄(Ⅰ)） 　　　Ideal formula : Fe. O 　　Actual formula : Fe 1 -XO (X≈0. 05) In the latter formula, Fe 3+ ions are present and O 2− vacancies are formed.

Why non-stoichiometry exists? Since the solid needs to be overall electrically neutral, the missing atom's charge needs to be compensated by a change in the charge for another atom in the solid, by changing the oxidation state, or by replacing it with an atom of a different element with a different charge.

Types of Defect • Schottky defect（ショットキー欠陥）: A pair of vacant sites, a cation defect and an anion defect 　（一対の陽イオンと陰イオンが抜ける） • Frenkel defect（フレンケル欠陥） : An atom displaced off its lattice site into an interstitial site 　（片方のイオンが格子間位置に移動） These defects are described using the Kroger-Vink notation.

Types of Defect • Schottky defect Cl Na Cl Na Cl Na Cl Na Cl Na Cl Na Cl Na Cl Na Cl Na At room temperature, only one in 1015 of both ion sites in Na. Cl is vacant.

Types of Defect • Frenkel defect Ag Cl Ag Cl Ag Ag Cl Cl C Ag Cl Ag Cl Ag

Kroger-Vink notation クレーガー･ビンク記号 • The symbol for the atom involved, or “V” if the site is vacant　　（空孔はVで表す） • A superscript indicating the net charge: “ ” for charge 1, “ ” for zero net charge, 　 “ ” for charge 1　　　　　（元に比べて“＋”の場合“ ” 、 ”－“の場合は“ ” 、変化なしの場合は“ ” ） • A subscript to indicated the nature of the site in an ideal crystal, with ” i” for an interstitial site and “s” for a surface site　（格子間位置は” i” )

Kroger-Vink notation Na. Na , Cl. Cl : Na+ and Cl ions on regular lattice sites, zero net charge VNa : a Na+ ion vacancy, net charge 1 Cl : a Cl ion vacancy, net charge 1 V Na Mgi : a substitutional Mg 2+ ion on a Na site, i charge +1 Ag : an interstitial Ag+ ion in Ag. Cl, charge 1 F : an interstitial F ion in Ca. F 2, charge 1

Other examples of Defects • Intrinsic defects: defects which are thermally created Example: Zn. O(Zn 1+x. O), Ni. O(Ni 1 -x. O) • Extrinsic defects: defects which are associated with dopants or impurities Example 1: Al 2 O 3 including Cr 2 O 3 Example 2: Zn. O including Al 2 O 3

Solid Solutions（固溶体） • A crystalline phase that can have variable composition　　　　　 (規則性なく組成が変化する結晶相） 　　　　　水とエタノールの混合と同じ！ Examples • Fe 0. 95 O : Mixtures of Fe. O and Fe 2 O 3 Problem 1: Calculate the molar fraction of each compounds in Fe 0. 95 O.

Answer to the problem The formation of Fe 0. 95 O is; x Fe. O + y Fe 2 O 3 →Fe 0. 95 O (x: mols of Fe. O in SS, y: mols of Fe 2 O 3 in SS) x+2 y=0. 95 ·····(1) x+3 y=1. 00 ·····(2) – (1); y=0. 05, x=0. 85 Answer: Fe. O = 0. 85 / 0. 90 = 94. 4 mol% Fe 2 O 3= 100 – 94. 4 = 5. 6 mol%

Types of Solid Solutions • Substitutional solid solutions (置換型) § The atoms or ions that is being introduced directly replaces an atom or ion in the parent structure • Interstitial solid solutions （格子間型） § The introduced species occupies a site that is normally empty and no ions or atoms are left out

Substitutional solid solutions • Al 2 -x. Crx. O 3 (0≤x ≤ 2) (derived from Al 2 O 3) § § § Al 3+ and Cr 3+ ions are distributed at random the probability that it is one or the other is related to the composition x. (each site is occupied by an ‘average cation’) Average cation whose properties, atomic number, size, etc. , are intermediate between those of Al 3+ and Cr 3+ ions 　(固溶体の物性値は、それぞれの値の 平均！) Example Ionic radius of a cation in Al 1. 6 Cr 0. 4 O 3 is calculated to be 69. 1 nm from ionic radii of Al 3+: 67. 5 nm and Cr 3+: 75. 5 nm.

Interstitial solid solutions • If the solute atoms are small, they may dissolve interstitially in the host crystal. § YF 3 in Ca. F 2 • Y 3+ is interstitially located in the lattice, and V • Ca is created. § Pd. Hx(0 ≤ x ≤ 0. 7) • Pd metal occludes(吸蔵する) H 2 gas, and H atoms occupy interstitial sites.

応用例1：Ba. Ti. O 3系サーミスタ PTC thernistor

Temperature-sensitive Resistors (Thermal Resistors : Thermistors) 6 5 NTC Thermistor 4 log(ρ/Ω m) • Negative temperature coefficient of resistance (NTC) • Positive temperature coefficient of resistance (PTC) 3 2 PTC Thermistor 1 Pt wire 0 0 40 80 T/ºC 120 160

Transformation of Ba. Ti. O 3 相変態 単斜晶 立方晶 菱面体晶 正方晶 6 5 NTC Thermistor log(ρ/Ω m) 4 3 2 PTC Thermistor 1 Pt wire 0 0 40 80 T/ºC 120 160

PTC Thermistors • Lanthanum-doped Ba. Ti. O 3(Ba 1 -XLa. XTi. O 3) or • Niobium-doped Ba. Ti. O 3 (Ba. Ti 1 -XNb. XO 3)

Defect chemistry of Ba. Ti. O 3 • In case of addition of La 2 O 3 and forming nonstoichiometric Ba. Ti. O 3 § Ba. O is formed or vacancies of Ti are formed. 　　 La 2 O 3 → 2 La • Ba + 2 Ba. O +2 e’ + 1/2 O 2 • + 2 V • • + 10 e’ + 1/2 O La O → 2 La 　　　 2 3 Ba Ti 2 • In case of addition of La 2 O 3 and forming stoichiometric Ba. Ti. O 3 § La 2 O 3(+2 Ti. O 2) La 2 O 3 → 2 La • Ba + 2 OXO +2 e’ + 1/2 O 2 • La • Ba is compensated by an electron ( 2 Ti. O 2 + 2 Ba. O → 2 Ba. XBa + 2 Ti. XTi + 6 OXO ).

Defect chemistry of Ba. Ti. O 3 • In case of another stoichiometric Ba. Ti. O 3 § Nb 2 O 5(+2 Ba. O) Nb 2 O 5 → 2 Nb • Ti + 4 OXO +2 e’ + 1/2 O 2 • In case of stoichiometric Ba. Ti. O 3 –Al 2 O 3(+2 Ti. O 2) Al 2 O 3 → 2 Al’Ti + 3 OXO +V • • O or Al 2 O 3 + 1/2 O 2 +2 e- → 2 Al’Ti + 4 OXO

Electroceramics 電子セラミックス Solid state chemistry 固体化学

Electroceramics and Solid State Cheminstry 電子セラミックスと固体化学 Application of Lattice Defects 格子欠陥の利用 学部　応用化学科　 片山　恵一 The End

Assignment Explain the relationship 　　　between electroceramics and crystal defects 　within 200 words or less. 　　　　　（日本語の場合は 500字以内） Submission deadline: Feb. 27 E-mail to: Katayama Keiichi<katakei@keyaki. cc. u-tokai. ac. jp>