Thermodynamic Optimization Of BaO-La₂O₃-TiO₂and BaO-Nd₂O₃-TiO₂Systems

The development and application of microwave dielectric ceramics were introduced in detail in this work, and the description for practical applications of the microwave dielectric ceramics based on BaO-TiO2with additions of rare-earth oxide (La2O3, Nd2O3) were made. The X-ray diffraction and differential scanning calorimetry methods were employed in this experimental work to carry out the meticulous detective about the phase identifications and relations of Ln2O3-TiO2(Ln=La, Nd) pseudo-binary system, meanwhile the phases La2Ti3O9、La4Ti3O12、 Nd2Ti3O9and Nd4Ti9024were identified, whose temperature ranges of existence were speculated according to the publications and the present experimental work. The phase diagram data from various detective methods were assessed comprehensively, during which the similarities and discrepancies were compared and analyzed. The CALPHAD technique was adopted for calculating La2O3-TiO2, Nd2O3-TiO2, BaO-La2O3, BaO-Nd2O3pseudo-binary systems, and BaO-La2O3-TiO2, BaO-Nd2O3-TiO2pseudo-ternary systems were thermodynamically extrapolated. The substitute solution models were used to describe the liquid phases and solution phases, and the rest of the phases were depicted via Neuman-Kopp rule. On the basis of the assessment of the phase diagram published, the over-all optimization was conducted about the systems mentioned above. A set of thermodynamic parameters were achieved which could reasonably describe the systems above within the experimental errors, and the calculated phase diagram employing these parameters agreed well with the published works. The thermodynamic database established in present work can provide solid references for the extrapolation of BaO-Nd2O3-Sm2O3-TiO2pseudo system.