基础材料和有机材料 (8).pdf

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1、(1)The formation conditions of substitutional solid solution and the factors affecting solid solubility.1.The size of ions2.Type of crystal structure3.Chemical valence of ions4.Electronegativity3.2 Substitutional solid solution1.The size of ionsr1and r2represent the radii of solvents and solute ions

2、 respectively.The relative difference of ion radii denoted asr.rrrr 1210.15rrrr 12130%rrrr 12115%30%Continuous solid solution may be formedOnly limited solid solution can be formedit is difficult or not able to form substitutional solid solution.Therefore,the larger difference for the size of the io

3、ns of theelements involved,the smaller for the solid solubility.0.0720.0610.07215.28%15%High temperature stable cubic phase,form continuous solid solutions.2.Type of crystal structureThe solute and solvent should have the same crystal structure orsimilar chemical formula,which is a necessary but not

4、 sufficientcondition for the formation of a continuous solid solution.NiO and MgO have face centered cubic structure and so they canform continuous solid solutions.MgO-CaO have the the same crystal structure,but r15%,sothey only form limited solid solutions.For PbZrO3and PbTiO3,the relative differen

5、ce of ion radius between Zr4+and Ti4+is 15.28%.0.06450.05350.064517.05%Fe2O3-Al2O3(0.0645nm and 0.0535nm),r of Fe3+and Al3+：Even through Fe2O3and Al2O3have the same corundum structure,only form limited solid solutions.Ca3Al2(SiO4)3and Ca3Fe2(SiO4)3have the same island likestructures and their crysta

6、l cells are eight times larger than oxide,which improved their structure tolerance.In this situationFe3+andAl3+can form continuous displacement.3.Chemical valence of ionsPb Fe NbOPbZrO12312533FeNbZr2354B-bit substitutionNaSiCaAl423In composite perovskite piezoelectric ceramic materialsNa BiTiOPbTiO1

7、212333NaBiPb121232The ions have the same chemical valence or the same sum ofchemical valence,a continuous solid solution may be formed.A-bit substitutionBesides in silicate crystal,the equivalent replacement ofcomposite ions often occurs.For,NaAlSi3O8-CaAl2Si2O8,Na+and Si4+are replaced by Ca2+andAl3

8、+at the same time.4.ElectronegativityElectronegativity is similar：it is conducive to form solid solution.Large difference in electronegativity:it tends to formcompounds.If the electronegativity difference is less than 0.4,it generally hasa large solid solubility,which is regard as a boundary to meas

9、urethe solid solubility.Above factors will affect the solid solubility,but they do notwork at the same time.Under some conditions,some factorsare the main factors.For example,even though the relativedifference between the radii of Al3+and Si4+is more than 45%,and the chemical values are different,bu

10、t the bond properties ofSi-O and Al-O are similar,so the solid solution can still beformed.In aluminosilicate,the phenomenon of replacement ofSi4+byAl3+is common.Generally,for oxide systems,the formation of solid solutionis mainly determined by the ion size and ion valence.1.DefinitionWhen solute io

11、n replaces solvent ion at the normal lattice sites,the unequal displacement may occur,and then the componentdefects will inevitably occur,such as the vacancy or the ionenters the gap sites.2.Factors affecting defects concentrationDifferent from thermal defects,the component defects ofsubstantial sol

12、id solution mainly depend on the doping amountand solid solubility.The solid solubility is generally only a fewpercent.(2)Component defects in substantial solid solutionForeign cation have higher valence than that of the normal host cation3.Type of component defects in substantial solid solution 22C

13、aClCaVClKClKKCl2 CaClCaClClKClKiCl2 CaOCaVOZrOZrOO 22CaOCaCaOZrOZriOForeign cation have lower valence than that of the normal host cationCation vacancy Interstitial anion Anion vacancy Interstitial cation 23423Al OAlVOMgAlOMgMgOA：Cation vacancy MgO and Al2O3can form magnesia alumina spinel,however,A

14、lrich spinel instead of pure spinel is usually obtained in thepreparation of magnesia alumina spinel by flame melting.In the process of spinel formation,a part of Mg2+in spinel isreplaced by Al3+and then form solid solution,so the aluminumcontent is higher.The defect reaction formula as follows:B：An

15、ion vacancy CaO dissolves in ZrO2,The defect reaction formula as follows:2 CaOCaVOZrOZrOOReasons for adding CaO：ZrO2have three crystal forms monoclinic,tetragonal andcubic.When the crystal form changes from monoclinic totetragonal,there is 7%9%s volume shrink,so it is not suitablefor thermostable materials.However,if CaO is added to ZrO2,ZrO2will be fixed in the high temperature cubic crystal withoutcrystal transformation,thus become very valuable thermostablematerials.