NEW DOUBLE BORATE Rb3HoB6O12: SYNTHESIS AND CHARACTERIZATION

Abstract

Objective. At the present time the interest of researchers has arisen to complex borates as selffrequency- doubling crystals, which combine laser and non-linear optical properties due to the presence of rare-earth elements and the borate matrix. Recently, we reported on the properties of the new noncentrosymmetric borates: Rb3NdB6O12 and Rb3EuB6O12. The main purpose of this paper is to synthesize and to characterize new double borate Rb3HoB6O12. Methods and methodology. In our study we use synthesis methods of solid state reaction and citrate sol-gel synthesis. Our analysis is based on X-ray powder diffraction method, differential scanning calorimetry and scanning electron microscopy. Results. Polycrystalline Rb3HoB6O12 was prepared by sol-gel synthesis. The purity of the double borate was confi rmed by X-ray powder diffraction analysis. While specimens obtained by solid– state reactions show Rb3HoB6O12 and small amount of impurity HoBO3. Indexing of the diffraction pattern of single-phase Rb3HoB6O12 by the isostructural compounds RbREB6O12 (RE = Nd, Eu) showed satisfactory results. Rb3HoB6O12 crystallized in space group R32 with unit cell parameters a = 13.4038(7), с = 30.315(2) Å, V = 4716.76 Å3. From differential scanning calorimetry measurements, the incongruent melting temperature Rb3HoB6O12 is observed at 818 °С. From scanning electron microscopy observations, single particles with sizes up to 100 μm formed by solid phase synthesis. The sol-gel synthesis resulted in the agglomerates 50–100 μm in size formed by strongly coalescent individual grains with a diameter below 2–3 μm. Conclusions. New double borate Rb3HoB6O12 were prepared by sol-gel synthesis. Obtained Rb3HoB6О12 is single-phase with average particle size of 50–100 μm. The unit cell volumes and the parameters Rb3REB6О12 (RE = Nd, Eu, Ho) correlate.

Keywords

• double borates rubidium and rare–earth elements
• solid-state synthesis
• citrate solgel synthesis.