Crystal Structure of Gd(Ca_3.319Sr_0.681)O[BO₃]₃ and Gd(Ca_2.592Sr_1.408)O[BO₃]₃

Abstract

The structure family of the rare‐earth calcium oxoborates RX2Z2$RX_{2}{Z}_{2}$O[BO3]3 (RCOB) has been investigated mainly with regard to their optical characteristics. Due to their monoclinic‐domatic structure they exhibit pyro‐ and piezoelectric properties, which is not dependent on the numerous possible substitutions of the rare‐earth cation site R. The rare‐earth cations are known to show partial disorder with the earth alkaline cation positions X and Z. To study whether a stabilization of the cation occupation is possible without disorder, calcium oxoborates are chemically modified using the Ca substitutes, Sr, Na, Y, Gd on the X and Z positions. No oxoborate phases can be synthesized by coupled substitution of Ca with Sr, Na, and a rare‐earth element. Only with single substitution of Sr the oxoborate phases can be synthesized. It is found that up to 35% Sr can be incorporated into the structure. From the synthesized Gd(Ca4−x$_{4-{{x}}}$Srx)O[BO3]3 precursor material, single crystals have been grown and used for the refinement of the first structure model. The structures have been refined in space group C1m1$C1m1$. A replacing only of Ca with Sr, mainly on the X position, has been observed. The stoichiometry resulting from the refinement is Gd(Ca3.319Sr0.681)O[BO3]3 and Gd(Ca2.592Sr1.408)O[BO3]3.

Novel Non-Centrosymmetric NdSr4O(BO3)3 Borate and Nd(Ca1−xSrx)4O(BO3)3 Solid Solutions: Preparation, Crystal Structures, Thermal Expansion and Optical Properties

“…Ions occupied these positions partially orderly: rare earths elements filled mainly the M1 positions, calcium-M2 and M3. Currently, there are studies of structures in which Ca 2+ ions are replaced by other metal ones, mainly Sr 2+ ; the effect of these substitutions on various properties has been studied [22][23][24]. According to Liu et al [22], the NLO properties of GdCa 4 O(BO 3 ) 3 crystals can be significantly improved by doping with 4% Sr 2+ .…”

“…The SHG efficiency achieved with Sr-doped and undoped GdCa 4 O(BO 3 ) 3 was 37 and 28%, respectively. It was shown in [24] that 35% of Sr ions can be incorporated instead of Ca into Gd(Ca 1−x Sr x ) 4 O(BO 3 ) 3 solid solutions. Moreover, by adjusting the Sr content in La(Ca 1−x Sr x ) 4 O(BO 3 ) 3 crystals (x = 0-0.4), the optical birefringence can be controlled and the blue light can be obtained in the range of 495-473 nm through type-I NCPM SHG of the corresponding fundamental wavelengths [23].…”

“…Wide ranges of Ca → Sr substitution are due to the closeness of the ionic radii of Ca 2+ and Sr 2+ (1.14 Å and 1.32 Å, respectively, for coordination number 6 [25]) and this maintains the congruent melting property, enabling the production of high-quality crystals. At the same time, the combination of coupled substitution with Na and REE is very limited, and the combination of Ca with Sr, Na and Gd could not be synthesized [24].…”

“…In addition, LnCOB has shown itself to be a promising material for efficient non-linear frequency conversion through non-critical phase matching (NCPM), and ongoing research is exploring its potential applications in optical technology [23]. The family of rare earth calcium oxoborates, LnCOB, contains promising candidates for pyro-and piezoelectric applications; their use is not limited to phase transitions [24]. Due to its congruent melting and absence of phase transitions, it can be grown from the melt directly and used in pyro-and piezoelectrics.…”

“…Here, in order to investigate the influence of cation substitutions on NLO properties and to expand the RCOB (R = REE) family, we report the results of synthesis and complex investigations of new NLO Nd(Ca 1−x Sr x ) 4 O(BO 3 ) 3 solid solutions and a new NdSr 4 O(BO 3 ) 3 compound. In the series of NdCa 4 O(BO 3 ) 3 compounds, it was possible to almost double the Ca → Sr substitution limits for Nd (x is approximately 0.7) in comparison to Gd (x = 0.35) and La (x = 0.4) [24]. In addition, a new non-centrosymmetric NdSr 4 O(BO 3 ) 3 compound obtained in the present studies can be considered as the prototype of a new REESr 4 O(BO 3 ) 3 series, where doped additives can be introduced into the position of a rare earth element to study the luminescent properties of these multifunctional materials.…”