Role of Nb2O5 phase in the formation of piezoelectric PbNb2O6

• PbNb2O6 (PNO) is piezoelectric with Curie temperature > 570 °C, only if orthorhombic.
• A difficult quenching from ∼1270 °C appeared essential to get the orthorhombic phase.
• DSC and XRD now show that monoclinic Nb2O5 gives orthorhombic PNO even on slow cooling.
• Quench-free preparation of this high temperature piezo-material is welcome.
• Done DSC and Rietveld XRD of two forms of Nb2O5 and two resulting phases of PNO.

Only the orthorhombic form of lead meta-niobate (PbNb2O6 or PNO) is ferroelectric, allowing high temperature piezoelectric applications. Quenching from a high temperature like 1270 °C appears essential to get the orthorhombic phase. But such quenching is risky and can generate defects in the sample. Here, differential scanning calorimetry (DSC) and XRD characterizations show that on using suitably pre-fired Nb2O5 or monoclinic Nb2O5 as starting reactant, slow cooling as well as quenching leads to orthorhombic PbNb2O6 as the product. Present work is the first detailed report of the preparation of orthorhombic PbNb2O6 without quenching. All starting materials, tried here, and resulting products have been thermally characterized along with necessary XRD characterizations.