Th e effect of sm all oxid e a dd itions on t he p olym orp hism of Bi,03 was studied by m eans of high-temperat ure x-ray diffrn,ctom etr y. Soli d us a nd occasiona l li q uidus temperatu res were approximated, so t hat te ntat ive partial phase diagra ms for 33 ox ide a dd ilions were con stru cted. Only t he m on ocli ni c a nd t he cubic f orms of B i, 0 3 were f ound to be stab le. Oth er phases, frequ en tly reported by p revious in vestigators, s uch as tetrago na l a nd bod ycentered cubic (b .c.c.), were shown to f orm m etastably fr om cooled liquid or eu bie. Au impure b. c.c. ph ase of distin ct but varia~~e e om pos i~i o n apI;eared in systems of ZnO,. Pb O, 1320 3, AI,03, Ga203, Fe, 0 3, S10 " GeO" 110 " a nd 1 , 0 5, lhe Im p ure b.c.c. p hase 111 t he s~' stem s with SiO" GeO" and Ti O, m elted congruently abo ut 100°C above the m .p. of 13 i,0 3' Th e im p ure b.c.c. p hase was f orm ed m etastably in s. vstems w it h R.b20, N iO, MnO, C d O, V, 0 5, an d Nb, 0 5; t he cond itions of fo rmation we re dependent on COHlposit ion, preparation, and heatin g sc hed ules. The impure b.c.c. p hases, bolh stabl e and metastable, had sm a ll er uni t cell dim ensions l han thal of pure Bi,0 3'

Stabili ty relationships of t he four p oly m orp hs of bismu t h oxide have been dct erJlIin ed by m eans of DTA a nd high-temperat ure x-ray studies. The stable low-temperature m onoclinic form t ransform s to the stabl e cubic form at 730 ± 5 ac, whi ch then m elts at 825 ± 5 ac.By controlled coolin g, t he m etastable tetragonal ph ase and/ o r t he metastable bod v-ce n te red cubic (b. c.c.) phase ap pear at about 645 ac. Wh ereas b. c.e. can be prese r ved to i·oom temperature, tetrago na l \\"ill transform to m onocli nic bct\\'een 550 a nd 500 ac. T etragona l Bi, 0 3, h owever, is easil y prepa red by decom posin g bismu t ite (B i, 0 3·CO,) at 400 ac for se vera l h ours. Th e g reatest transit ion expa nsion occurs at t h e m on ocl inic to cubic in versio n, an d cubi c 13i,03 shows t he g reatest coeffi cient of vo lum e expansion. vVi th exposure to a ir, 13 i, 0 3 carbo nates a nd pa r tiall y t ra nsforms to bismu tite a nd a n u nkno,yn ph ase.

The phase diagram for the system Bi2O3‐B2O3 has been determined experimentally. The melting point of Bi2O3 has been redetermined as 825° C with an estimated overall uncertainty of about ±3°C, and the molal heat of fusion of Bi2O3, calculated from the slope of the liquidus curve, is 2050 cal per mole. The system contains a body‐centered cubic phase of approximate composition 12Bi2O3·B2O3, which melts incongruently at 632°C. Four congruently melting compounds exist in the system: 2Bi2O3· B2O3·5B2O3, Bi2O3·3B2O3, and Bi2O3·4B2O3, with melting points, respectively, of 675°, 722°, 708°, and 715°C. The Bi2O3·4B2O3 compound exhibits a sluggish transformation at 696°C. Compositions containing up to 97.5 wt% (85 mole %) Bi2O3 can be partly or totally quenched to glass. Indices of the quenched glasses are greater than 1.74. A region of liquid immiscibility extends at 709°C from almost pure B2O3 to 19.0 mole % Bi2O3. The extent of immiscibility theoretically calculated agrees with the experimentally determined value when 1.20 A is used for the ionic radius of Bi3+.

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.

A phase equilibrium diagram of the system BaO-B20 3 has been constructed fr om data obtained essentiall y by the quenching method. Four congruently m elting compounds were identifi ed: BaOAB20 3, melting at 879° ± 5° C; BaO.2B20 3, melting at 900° ± 5° C; BaO.B20 3, melting at 1,095° ± 5° C; and 3BaO.B20 3, melting at 1,383° ± 5° C . Some optical properties of these compounds were determined with the petrographic microscope, and X-ray d.ffraction data suitable for their id entification were obtained. Barium m etaborate, BaO.B20 3, s howed an inversion occurring between 100° and 400° C. Mixtures contain ing less than 30 p ercent of BaO were found to eparate on fu sion into two li quid layers, one of which contained 30 p ercent of BaO, wherea t he other was nearly pure 1320 3• A curve showing indices of refraction of the quenched glasses is also presc ntcd.