Li2Sr4B12O23: A new alkali and alkaline-earth metal mixed borate with [B10O18]6− network and isolated [B2O5]4− unit

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Abstract

A novel ternary lithium strontium borate Li2Sr4B12O23 crystal with size up to 20 mm×10 mm×4 mm has been grown via the top-seeded solution growth method below 730 °C. Single-crystal XRD analyses showed that Li2Sr4B12O23 crystallizes in the monoclinic space group P21/c with a=6.4664(4) Å, b=8.4878(4) Å, c=15.3337(8) Å, β=102.02(3)°, Z=2. The crystal structure is composed of [B10O18]6− network and isolated [B2O5]4− unit. The IR spectrum further confirmed the presence of both BO3 and BO4 groups. TG-DSC and Transmission spectrum were reported. Band structures and density of states were calculated.

Graphical abstract

A new phase, Li2Sr4B12O23, has been discovered in the ternary M2O–M′O–B2O3 (M=alkali-metal, M′=alkalineearth metal) system. The crystal structure consists of [B10O18]6− network and isolated [B2O5]4− unit.

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Highlights

► Li2Sr4B12O23 is a a novel borate discovered in the M2O–M′O–B2O3 (M=alkali-metal, M′=alkaline-earth metal) system. ► Li2Sr4B12O23 crystal structure has a three-dimensional crystal structure with [B10O18]6− network and isolated [B2O5]4− unit. ► Sr1 and Sr2 are located in two different channels constructed by 3[B10O18] network.

Introduction

Because of the relatively high resistance against laser-induced damage and higher transparency in the UV region, borate nonlinear optical (NLO) crystals are often employed for high-power UV light generation [1], [2], [3]. Alkali or alkaline-earth metal borates, such as LiB3O5 (LBO) [4], CsB3O5 (CBO) [5], CsLiB6O10 (CLBO) [6], β-BaB2O4 (BBO) [7], KBe2BO3F2 (KBBF) [8] and K3B6O10X (X=Cl, Br) [9], [10] are outstanding NLO materials for efficient second harmonic generation (SHG) of Nd:YAG lasers, which induces a considerable interest in search for new promising compounds in ternary borate systems M2O–M′O–B2O3 (M=alkali metal, M′=alkaline-earth metal) [11], [12], [13], [14], [15], [16], [17], [18], [19]. The alkali or alkaline-earth metal cations are ideal candidates for the UV NLO borate because they can favor excellent optical transparency in the UV spectral region [20]. Hence, some new compounds may also be expected to exist in alkali and alkaline-earth metal mixed borates. Extensive efforts in the M2O–M′O–B2O3 ternary system lead to a new phase, Li2Sr4B12O23 (LSBO), which is a novel borate featuring [B10O18]6− network and isolated [B2O5]4− unit. Herein we report the crystal growth, structure and optical properties of LSBO for the first time.

Section snippets

Sample preparation and the synthesis of compound

Single crystal of LSBO was grown by the top-seeded solution growth (TSSG) method in a PbO–PbF2 flux system. All reagents were of analytical grade, Li2CO3 (5.9112 g, 0.08 mol), SrCO3 (5.9052 g, 0.04 mol), H3BO3 (17.3124 g, 0.28 mol), PbO (4.464 g, 0.02 mol) and PbF2 (4.9038 g, 0.02 mol) were precalcined at 300 °C and 600 °C for 4 h, respectively, to decompose the boric acid and carbonates. After that the mixture was loaded in the Pt crucible, heated to 830 °C and kept for 10 h to ensure the powder was melted

Description of the structure

Single-crystal X-ray diffraction data show that LSBO crystallizes in the monoclinic system with space group P21/c. The basic boron–oxygen structural unit in LSBO are [B10O18]6− network and isolated [B2O5]4− unit (Fig. 2). One BO4 unit is connected by two BO3 and two BO4, forming two almost vertical connecting penta-borate unite [B5O9]3−, and two vertex-connected [B5O9]3− unites further compose [B10O18]6− unit. Four [B10O18]6− units are interconnected by O8, forming three-dimensional 3[B10O18]

Conclusions

A novel ternary borate with the composition Li2Sr4B12O23 has been synthesized. It has a three-dimensional structure composed by [B10O18]6− network and isolated [B2O5]4− unit, bridged by Li and Sr cations. LSBO decomposes into SrB2O4 and LiBO2 at 794 °C, binary PbO and PbF fluxes were introduced to grow sizable crystal. The ultraviolet cutoff edge for the LSBO crystal is 290 nm. The results of LDA calculations indicate optical properties mainly result from the basic boron–oxygen structural unit in

Acknowledgments

This work is supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China (Grant Nos. 200821159, 2009211B33). Main Direction Program of Knowledge Innovation of Chinese Academy of Sciences (Grant Nos. KJCX2–EW–209–3, KJCX2–EW–H03–03), the “National Natural Science Foundation of China” (Grant Nos. 50802110, 21001114), the “One Hundred Talents Project Foundation Program” of Chinese Academy of Sciences, the “Western Light Joint Scholar Foundation” Program of Chinese

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