title: Formation Mechanisms in β-Ca3(PO4)2-ZnO Composites: Structural Repercussions of Composition and Heat Treatments.
abstract: Composites with varied proportions of β-Ca3(PO4)2and ZnO were obtained through an in situ aqueous precipitation method under slightly basic (pH ≈ 8) conditions. The formation of β-Ca3(PO4)2phase starts at an early heat-treatment stage (∼800 °C) and incorporates Zn2+ions at both Ca2+(4) and Ca2+(5) sites of the lattice up to its occupancy saturation limit. The incorporation of Zn2+in the β-Ca3(PO4)2lattice enhances its thermal stability delaying the allotropic β-Ca3(PO4)2→α-Ca3(PO4)2phase transformation. The excess zinc beyond the occupancy saturation limit precipitates as Zn(OH)2and undergoes dehydroxylation to form ZnO at elevated temperatures. The presence of ZnO in the β-Ca3(PO4)2matrix yields denser microstructures and thus improves the mechanical features of sintered composites up to an optimal ZnO concentration beyond which it tends to exert an opposite effect.
authors.affiliation: Centre for Nanoscience and Technology, Pondicherry University , Puducherry 605 014, India.
authors.forename: Ponnusamy
authors.initials: P
authors.lastname: Nandha Kumar
authors.affiliation: Department of Materials and Ceramics Engineering, University of Aveiro, CICECO , Aveiro 3810 193, Portugal.
authors.forename: José Maria da Fonte
authors.identifier: http://orcid.org/0000-0002-7520-2809
authors.initials: JM
authors.lastname: Ferreira
authors.affiliation: Centre for Nanoscience and Technology, Pondicherry University , Puducherry 605 014, India.
authors.forename: Sanjeevi
authors.identifier: http://orcid.org/0000-0003-2285-4907
authors.initials: S
authors.lastname: Kannan