pH Controlled
Pathway and Systematic Hydrothermal
Phase Diagram for Elaboration of Synthetic Lead Nickel Selenites
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Abstract
The PbO–NiO–SeO<sub>2</sub> ternary system was fully
studied using constant hydrothermal conditions at 473 K. It yields
the establishment of the corresponding phase diagram using a systematic
assignment of reaction products by both powder and single-crystal
X-ray diffraction. It leads to the preparation of three novel lead
nickel selenites, α-PbNi(SeO<sub>3</sub>)<sub>2</sub> (<b>I</b>), β-PbNi(SeO<sub>3</sub>)<sub>2</sub> (<b>II</b>), and PbNi<sub>2</sub>(SeO<sub>2</sub>OH)<sub>2</sub>(SeO<sub>3</sub>)<sub>2</sub> (<b>III</b>), and one novel lead cobalt selenite,
α-PbCo(SeO<sub>3</sub>)<sub>2</sub> (<b>IV</b>), which
have been structurally characterized. The crystal structures of the
α-forms <b>I</b>, <b>IV</b>, and <b>III</b> are based on a 3D complex nickel selenite frameworks, whereas the
β-PbNi(SeO<sub>3</sub>)<sub>2</sub> modification (<b>II</b>) consists of nickel selenite sheets stacked in a noncentrosymmetric
structure, second-harmonic generation active. The pH value of the
starting solution was shown to play an essential role in the reactive
processes. Magnetic measurements of <b>I</b>, <b>III</b>, and <b>IV</b> are discussed