Synthesis, Crystal Structure, and Characterizations of Two Tantalum Phosphates A₃TaP₂O₉ (A=K, Na)

Abstract

Two new compounds K 3 TaP 2 O 9 and Na 3 TaP 2 O 9 were obtained by spontaneous crystallization with KH 2 PO 4 and K 2 HPO 4 or NaH 2 PO 4 and Na 2 HPO 4 as fluxes, respectively. K 3 TaP 2 O 9 belongs to the P2 1 /m space group of the monoclinic system, with cell parameters of a = 9.8912(7) Å, b = 7.1861(5) Å, c = 13.6457(9) Å, β = 94.047(2)°, and Z = 4. In contrast, Na 3 TaP 2 O 9 pertains to the P2 1 2 1 2 1 space group of the orthorhombic system, with cell parameters of a = 7.1241(7) Å, b = 9.3071(10) Å, c = 12.3752(13) Å, and Z = 4. Both of the structures feature the existence of the zigzag (TaP 2 O 9 ) ∞ chains with the −(O 4 Ta)−O−(TaO 4 )− connection. Also, two compounds have high transparency of about 90% in the 400−2500 nm range. Theoretical calculations and powder second-harmonic generation test show that the compound Na 3 TaP 2 O 9 has a large band gap of 5.5 eV, a moderate powder second-harmonic generation response of 0.6 × KDP, and a large birefringence of 0.11.

Na11Ta8P7O43: (Ta8O33) bi-capped triangular prisms connected by PO4 groups resulting in a phase-matched second harmonic response

“…12 A related scientific research study to explore the octahedralcoordinated d 0 transition metal phosphate system has been in progress. In 2022, two kinds of non-centrosymmetric tantalum phosphate crystals, Na 3 TaP 2 9 13 and Na 5 were thoroughly mixed at masses of 2.0 g, 1.8 g and 0.5 g, respectively, and placed into a platinum crucible. Then, the crucible was placed in a programmable electric furnace, heated to 850 °C and kept for 24 hours to melt the content completely.…”

“…A related scientific research study to explore the octahedral-coordinated d 0 transition metal phosphate system has been in progress. In 2022, two kinds of non-centrosymmetric tantalum phosphate crystals, Na 3 TaP 2 O 9 13 and Na 5 Ta 8 P 5 O 35 , 14 were discovered by our group. Both crystals had the characteristics of phase-matchability, a large band gap, a wide transmission range and high transmittance.…”