RbMT₃(BO₃)₂O₃ (M=Ba, Sr; T=Al, Ga): New Double‐Layered Oxyborates Constructed from [BO₃] Triangles and [TO₄] Tetrahedra

Abstract

Four new alumino‐/galloborates RbMT3(BO3)2O3 (M=Ba, Sr; T=Al, Ga) have been synthesized for the first time by using a high‐temperature solution method. All the title compounds have Sr2Be2B2O7‐like structures, in which the [BO3] triangles and [TO4] tetrahedra form the final double‐layered configurations with the M‐ and Rb‐site atoms located between and in the double layer, respectively. The structure evolution from Sr2Be2B2O7 to RbMT3(BO3)2O3 series is discussed. The broader energy bandgaps in Al‐based borates when compared with Ga‐based ones can be entirely attributed to the location of Al/Ga s orbitals near the Fermi surface. Both experimental and computational approaches were used to study their structure‐property relationships.

Tailored Synthesis of Two Metal Borates KSrM3B2O9 (M = Al and Ga) Exhibiting Wide Ultraviolet Transparency

“…Additionally, the stretching and bending vibrations of [Al/GaO 4 ] tetrahedra are responsible for the peaks below 600 cm –1 . These assigned observations of KSrAl 3 B 2 O 9 and KSrGa 3 B 2 O 9 are consistent with the previously reported results, further confirming the rationality of structural analyses. ,,, …”

“…As presented in Figure a,b, the UV cutoff edges of KSrAl 3 B 2 O 9 and KSrGa 3 B 2 O 9 are approximately at 194 and 200 nm, respectively. Remarkably, the KSrAl 3 B 2 O 9 compound can penetrate in the deep UV band, exhibiting a transmittance of approximately 24% at 194 nm, which is comparable to that of the derivatives such as RbBaAl 3 (BO 3 ) 2 O 3 and RbSrAl 3 (BO 3 ) 2 O 3 . Based on the Kubelka–Munk formula equation, the corresponding experimental band gaps of KSrAl 3 B 2 O 9 and KSrGa 3 B 2 O 9 were found to be approximately 5.47 and 4.83 eV, respectively (inset of Figure a,b).…”

“…Remarkably, the KSrAl 3 B 2 O 9 compound can penetrate in the deep UV band, exhibiting a transmittance of approximately 24% at 194 nm, which is comparable to that of the derivatives such as RbBaAl 3 (BO 3 ) 2 O 3 and RbSrAl 3 (BO 3 ) 2 O 3 . 25 Based on the Kubelka−Munk formula equation, 26 the corresponding experimental band gaps of KSrAl 3 B 2 O 9 and KSrGa 3 B 2 O 9 were found to be approximately 5.47 and 4.83 eV, respectively (inset of Figure 3a,b). Furthermore, the infrared (IR) spectral analyses depicted in Figure 3c,d demonstrate that both title compounds exhibit comparable characteristic peaks.…”

“…For example, aluminum borates BaAl 2 B 2 O 7 , SrAl 2 B 2 O 7 , K 2 Al 2 B 2 O 7 , and β-Rb 2 Al 2 B 2 O 7 2 consist of isolated [BO 3 ] triangles and [AlO 4 ] tetrahedra, showcasing a favorable deep UV absorption edge below 200 nm. Aluminum/gallium borates RbMAl 3 (BO 3 ) 2 O 3 (M = Ba and Sr) and RbMGa 3 (BO 3 ) 2 O 3 (M = Ba and Sr) exhibit an intriguing double-layered structure, analogous to those of Sr 2 Be 2 B 2 O 7 . It is evident that the Al and Ga elements, belonging to the main group identical to that of boron, exhibit a remarkable propensity for facile construction of rigid [AlO 4 ] and [GaO 4 ] tetrahedral frameworks.…”

Structural Motif Cosubstitution Strategy for Designing Fluoroaluminoborate with the Sr2Be2B2O7-Type Double-Layered Structure

“…Moreover, the [Al 2 B 6 O 14 F 4 ] units are filled in the interlamination to replace the bridging oxygen and used to connect the two 2 ∞ [Al 1.18 B 2.82 O 8 ] layers to construct 2 ∞ [Al 4.36 B 11.64 O 26 F 4 ] double layers. Based on the thorough survey, varied structural motifs filled in interlamination of double-layer structures can be found in borates (Figure S2 in the Supporting Information), such as bridging O/F in Cs 2 Al 2 (B 3 O 6 ) 2 O and K 3 N 3 Li 2 Al 4 B 6 O 20 F (N = Sr, Ba), , [BO 3 ] units in CsBaB 9 O 15 and RbMT 3 (BO 3 ) 2 O 3 (M = Ba, Sr; T = Al, Ga), , [B 2 O 5 ] units in M 2 Cd 3 B 16 O 28 (M = Rb, Cs) and Cs 2 K 2 B 10 O 17 , , [B 3 O 7 ] units in PbLnB 7 O 13 (Ln = Tb or Eu), [B 9 O 18 ] units in Na 11 B 21 O 36 X 2 (X = Cl, Br), 1 ∞ [B 6 O 12 ] infinite chains in AgSrB 7 O 12 and Sr 3 B 14 O 24 . , In addition, there are also some successful cases of various structural motif linkers filled in the single-layer structures. , As far as we know, the [Al 2 B 6 O 14 F 4 ] unit as a structural motif linker filled in interlamination of double-layer structure in Sr 2 Al 2.18 B 5.82 O 13 F 2 is the first case in borates, which greatly enriches the structural chemistry of layered borates.…”