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.

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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 .

The phase eq uilibrium re lation ships of th e Ti02·Ta20 , system were determined in air. An equi· molar co mpound , TiTa2O" was found to me lt congru ently at about 1662 °e and have a monoclinic unit cell a = 20.297 A, b = 3.804 A, c = 11 .831 A, f3 = 120°14', apparently isostnictural with TiNb20,.In addition, two othe r compound s are postulated to occ ur at about Ti02:49Ta20 , and Ti02: 7Ta20 s and to dissociate at about 1230 and 1190 °e, respec tively. Ti02 apparently accepts a maximum of 9 mole pe rce nt T a20s in solid solution at 1630 0c. Two eutecti cs occ ur in the syste m at 54 mole perce nt Ta20, and 1650 °e and 31 mole percent TazOs and 1630 0c.

The phase equilibrium diagram for the system Laz03-Bz03 has been determined experimentally. The compounds Laz03.3Bz03 and Laz03.-BzO3 melt congruently at 1141" f 5°C. and 1660" f 15"C., respectively. At 1488' f SOC., Laz03.-Bz03 inverts from the aragonite-type structure to a high-temperature form. Trilanthanum borate, 3LaZO3.BZO3, melts incongruently at 1 3 8 6 O f 5OC. to give liquid and La208. No solid solutions exist in the system. A region of liquid immiscibility exists in the system and extends at 1136' f 5°C. from almost pure B 2 0 3 to 21.5 mole ' % La203. The eiperimental value for the extent of immiscibility agrees with that calculated from theoretical considerations. A second method for estimating immiscibility in the system is demonstrated, which requires experimentally only the determination of t h e index of refraction of the modifier-rich liquid. FVinciples governing immiscibility are discussed.