Spark Plasma Sintering of Ceramics Based on Solid Solutions of Na<sub>1+2x</sub>Zr<sub>2−x</sub>Co<sub>x</sub>(PO<sub>4</sub>)<sub>3</sub> Phosphates: Thermal Expansion and Mechanical Properties Research
A. A. Aleksandrov,
A. I. Orlova,
D. O. Savinykh,
M. S. Boldin,
S. A. Khainakov,
A. A. Murashov,
A. A. Popov,
G. V. Shcherbak,
S. Garcia-Granda,
A. V. Nokhrin,
V. N. Chuvil’deev,
N. Yu. Tabachkova
Affiliations
A. A. Aleksandrov
Materials Science Department, Physical and Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603022 Nizhny Novgorod, Russia
A. I. Orlova
Materials Science Department, Physical and Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603022 Nizhny Novgorod, Russia
D. O. Savinykh
Materials Science Department, Physical and Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603022 Nizhny Novgorod, Russia
M. S. Boldin
Materials Science Department, Physical and Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603022 Nizhny Novgorod, Russia
S. A. Khainakov
Faculty of Chemistry, University of Oviedo, 33003 Oviedo, Spain
A. A. Murashov
Materials Science Department, Physical and Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603022 Nizhny Novgorod, Russia
A. A. Popov
Materials Science Department, Physical and Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603022 Nizhny Novgorod, Russia
G. V. Shcherbak
Materials Science Department, Physical and Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603022 Nizhny Novgorod, Russia
S. Garcia-Granda
Faculty of Chemistry, University of Oviedo, 33003 Oviedo, Spain
A. V. Nokhrin
Materials Science Department, Physical and Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603022 Nizhny Novgorod, Russia
V. N. Chuvil’deev
Materials Science Department, Physical and Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603022 Nizhny Novgorod, Russia
N. Yu. Tabachkova
Center Collective Use “Materials Science and Metallurgy”, National University of Science and Technology “MISIS”, 119991 Moscow, Russia
The structure, microstructure, coefficient of thermal expansion (CTE), and mechanical properties of Na1+2xZr2−xCox(PO4)3 ceramics (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were studied. Na1+2xZr2−xCox(PO4)3 submicron powders with the NaZr2(PO4)3 structure (NZP, kosnarite type) were obtained by the solid-phase method. The starting reagents (NaNO3, ZrOCl2·8H2O, NH4H2PO4, CoCl2·6H2O, ethanol) were mixed with the addition of ethyl alcohol. The resulting mixtures were annealed at 600 °C (20 h) and 700 °C (20 h). The obtained phosphates crystallized in the expected structure of the NaZr2(PO4)3 type (trigonal system, space group R3¯c). Thermal expansion of the powders was studied with high-temperature X-ray diffraction at temperatures ranging from 25 to 700 °C. CTEs were calculated, and their dependence on the cobalt content was analyzed. Na1+2xZr2−xCox(PO4)3 ceramics with high relative density (93.67–99.70%) were obtained by Spark Plasma Sintering (SPS). Ceramics poor in cobalt (x = 0.1) were found to have a high relative density (98.87%) and a uniform fine-grained microstructure with a grain size of 0.5–1 µm. Bigger cobalt content leads to a smaller relative density of ceramics. During the sintering of ceramics with high cobalt content, anomalous grain growth was observed. The powder compaction rate was shown to be determined by creep and diffusion intensity in the Na1+2xZr2−xCox(PO4)3 crystal lattice. SPS activation energy in ceramics increased as the cobalt content grew. The microhardness and fracture toughness of ceramics did not depend on their cobalt content.
