Engineered low temperature hydrothermal synthesis of phase-pure lead-based perovskites using ethylenediamine tetra-acetic acid complexation

Thermodynamic modeling of hydrothermal solutions was used to examine the influence of ethylenediamine tetra-acetic acid (EDTA) on the synthesis of lead-based perovskites, PbTiO₃ and PbZr_0.52Ti_0.48O₃. Temperature, pH, input reagent concentrations, and Pb/(Ti + (Zr)) and Pb/EDTA ratios were examined. Thermodynamic calculations from 25 to 100 °C indicated that, when the Pb/EDTA and Pb/(Ti + (Zr)) molar ratios were 2.0 and Pb input concentration was 0.1 m, phase-pure perovskites formed across the greatest pH range (7-14+). Precipitation of unwanted unary lead phases such as PbO was suppressed in all cases. In the absence of EDTA and solutions containing a molar excess of lead ions, the formation of phase-pure perovskites was limited to narrow pH ranges (5-8 and above 14) because of PbO precipitation. Theoretical predictions were experimentally validated with use of X-ray diffraction, transmission electron microscopy, energy dispersive spectrometry, and atomic absorption spectroscopy. Experimental results validated the theoretical predictions at temperatures above a minimum reaction temperature. Relative to comparable hydrothermal systems free of EDTA, the addition of EDTA was found to lower the minimum reaction temperature by 70 °C for PbTiO₃ (70 °C) and 25 °C for PbZr_0.52Ti_0.48O₃ (125 °C).