Deep-ultraviolet
(deep-UV) nonlinear optical (NLO) phosphates have
become a continuing hot spot since the discovery of Ba3P3O10X. Herein, we report two new deep-UV NLO
phosphates, KZn(PO3)3 and RbZn(PO3)3, crystallizing in the asymmetric R3 (No. 146) space group with a three-dimensional (3D) network constructed
by [PO3]∞ chains and distorted C
3v
[ZnO6] octahedra.
Both compounds exhibit phase-matchable behaviors with relatively strong
powder SHG intensities (about 0.6× and 0.7× those of the
benchmark KDP) and short deep-UV cutoff edges (<200 nm). First-principles
calculations reveal the synergy of the distorted [ZnO6]
octahedron and the flexible [PO3]∞ chain
that contribute respectively to the d
16 value by 14 and 84% in KZn(PO3)3 or 6 and
93% in RbZn(PO3)3. Remarkably, the SHG-active
[ZnO6] herein is pointed out for the first time, which
offers an unconventional access to the design and searches for deep-UV
NLO material candidates.
The structure–property relationship
has always been the
foundation of material design. Herein, we report two new cyclotetraphosphates
containing no rare earth element, cubic CsBi(P4O12) and its isostructural RbBi(P4O12). Single
crystal diffraction data reveal their I
3d structures featuring the isolated
cyclic [P4O12] building blocks with multiple
orientations. Interestingly, compared to the monoclinic linear chain
CsBi(PO3)4, the symmetry change caused by the
cycling of the [PO4] tetrahedral building units give rise
to a strong NLO response in a non-phase-matching behavior with a maximum
SHG intensity about 4.2 times that of KDP that agrees well with the
DFT calculation results (static d
36 =
4.917 pm/V). More insightfully, the cyclomerization of the [PO4] tetrahedral building unit also associates with the anionic
condensation, which may be responsible for the excellent bulk ionic
conductivity of 2.91 × 10–5 S·cm–1 at 383 K, with an activation energy of only 0.18 eV, which is one
of the lowest values among phosphates.
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