No abstract

A classification of A +2 B+'03 com pounds has been made on t he basis of ionic radii of the cons tituent ions. A grap h of t his type for t he perovski te compounds can be ~ivide d in~o orthor hombic, pseud ocubic, a nd cubic fi elds, wit h an area of ferroelectn c and antlferroelectnc compounds s uperimposed on the cuhic fi eld . The structures of s ohd solutIOns . be~ween vari ous perov s ki te compou nds cannot b e completely c<;)JT el~ted on the basIs

Selected mixtures in 69 binary systems involving Ab03, Ga20 a, CrZ0 3, Fe20 a, SczOa, In20 3, Y20 3, and the rare earth oxides were stud ied by X-ray diffraction techniques after heat treatment at various temperatures. A plot of the radii of the A +3 cations versus the radii of B+3 cations shows the regions of stability for the different structure types found for Ithe double oxides of the trivalent cations. The following structure types were encoun tered: A, B, and C-type rare earth oxide; corundum, beta gall ia; kappa alum ina; garnet; perovskite; and several types which could not be d efinite ly re lated to known structures. The majority of A+3 B+3 0 3 compounds have the perovskite structure. Several phases, including (1-x)Fez0 3·xAh03 ., and (1-x) Fe,03·xGa20 3 ." appear to have structures s imi lar to kappa alumina. Solid solution dcfin itely occurs in many of t he garnet type compounds which contain gailia. Based on the data collected in this survey, the s ubsolidu s phase equi libria re lationships of 79 binary systems were drawn.

T~e phase eq ui libr. iu m diag ram fo r th c binary sy ste m bis mu t h sesq uioxide-niobium pentoxlde has been cO llsLru cted from obse rvaL iolls of fu sion characteristics a nd X-ray diffracbon data. In t he syste m fi ve blila ry compounds were obse rved wi t h Bi20 3 :NbzOs ratios of .5: 3, 1 : 1. 4: D, 1: 5, a nd 1 : 6. The 1: 1 co mpo und was fou nd to Lransform irreversibl y (Ill la borator y t une) from t he ort horh ombic bis l11u totantali tc typc st ruc t ure to a tricli nic fo rm at about 1,020 °C and me lt congrue ntl y at J ,24 . 5 °C. The 5:3 com pound melts in congru e nt ly at 1,193 °C t he 4: 9 at 1,183 °C a nd the 1: 6 at 1,242 °C. The J : 5 co mpou nd h as a max imum t e mpe rat ure of stab ili ty at 1,095 °C alld Liw 4:9 a nd J: 6 co mpound have minimum te mperatures o~ st~b ili~y at 1,070 °C and 1, 002 °C res pectivc ly. Nb20 s was found to ?ntcr m to sohd solu tIOn In BI20 ,! up t? about 23 .5 mo le pc rce nt Nb20 s. The me lting p oint I S lllcreased and the monoc linic-cub ic phasc t ra ns form ation tem perat ure is decreased . A morphotropIC phase change OCC UlTS at about 19.5 mole pe rccnt NbzOs from the cubic to a p se udocu bic st ru cture .

Th e polymorphi c relatioll ships of t he pure rare-carlh oxides have been r ei nves tigated us ing X-ray diffrac tion methods for ident ificat ion of phases. The ox ides of the t rivalen t rare eart h ions crystalli ze in t hree different typ es: A rt B, and C. Each oXIde has o nly one t ruly stab le polymorph: La203, Ce20 3, Pr20 3, a nd Nd2 u 3 belong to the A type ; Sm 20 3, Eu20 3, a nd Gd20 3 to t he B type; Tb20 3, Dy20 3, H020 3, E1"20 3, Tm20 3, Yb20 3, and LU 20 3 to t he C ty pe. In addition Nd20 3, Sm20 3 EU 20 3, and Gd20 3 have .low-te mpcrature, appare ntly metastable, C-type pol ymo rphs. 1.~h e low-te mperat ure fOt"lTI lI~verts IITcvers lbl.v to the stab le form at in creas in gly hi gher temperatures fo r dec rea sIn g catIOn radlLl s.