Structures, Thermal Behaviors, and Luminescent Properties of Anhydrous Lanthanum Iodate Polymorphs

Abstract

The structural and thermal studies of six anhydrous lanthanum iodate polymorphs are presented. The variation of the [IO3(-)]:[La(3+)] molar ratio in the starting solution and the evaporation rate of the solution leads to either the centric La(IO3)3(HIO3) or the acentric La(IO3)3(HIO3)1.33 phases. The crystal structure of La(IO3)3(HIO3)1.33 was determined. The thermal treatments of these two phases up to 490 °C lead to β-La(IO3)3, observed at room temperature. To better understand the similar thermal behaviors of La(IO3)3(HIO3)1.33 and La(IO3)3(HIO3) compounds and their structural evolution, thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC) analyses and in situ temperature-dependent powder X-ray diffraction (XRD) experiments were carried out. These experiments allowed us to highlight the successive formation of δ-La(IO3)3 and γ-La(IO3)3. δ-La(IO3)3 is observed from the beginning of thermal decomposition of La(IO3)3(HIO3)1.33 (at 340 °C) or La(IO3)3(HIO3) (at 300 °C) up to 440 °C. A phase transition from δ-La(IO3)3 to γ-La(IO3)3 then occurs at 440 °C. Finally, the phase transition from γ-La(IO3)3 to β-La(IO3)3 occurs at 140 °C. A cycle of heating and cooling shows the reversible phase transition at 185 and 140 °C, respectively. β-, γ-, and δ-La(IO3)3 are three polymorph phases of the first α-La(IO3)3 already characterized. The structure of β-La(IO3)3 and γ-La(IO3)3 were determined on powder XRD analyses. The iodate compounds present a very broad domain of transparency from the visible range to the beginning of the far-infrared range. The intensities of SHG light generated by α-La(IO3)3, β-La(IO3)3, La(IO3)3(HIO3)1.33, and α-LiIO3 compounds with acentric structures were compared: β-La(IO3)3 < La(IO3)3(HIO3)1.33 < α-La(IO3)3 ≈ α-LiIO3. Finally, the luminescence spectroscopy of La(IO3)3(HIO3)1.33:Nd(3+), α-La(IO3)3:Nd(3+), and α-La(IO3)3:Yb(3+) is studied.

K2Au(IO3)5 and β‐KAu(IO3)4: Polar Materials with Strong SHG Responses Originating from Synergistic Effect of AuO4 and IO3 Units

“…À ions as those in a-KAu(IO 3 ) 4 (P1) reported by Albrecht-Schmitt et al, [23] but the local symmetry of the [Au(IO 3 ) 4 ]…”

“…Compared with compound 2,c ompound 1 is more sensitive to the synthetic conditions and requiredasmaller amount of Au(OH) 3 but al argera mount of I 2 O 5 .T he reported aKAu(IO 3 ) 4 may by present in the product randomly in av ery low yield along with al arger amounto fc ompound 2,b ut as ingle phase of a-KAu(IO 3 ) 4 has not been isolated by now on the basis of our experiments. For the preparations of the pure phases of both compounds 1 and 2,alargee xcesso fK IO 3 is necessary.I tw as found that colorless K(IO 3 )(HIO 3 )c rystals were easily grown when the reactionp roducts were cooled to room temperature.…”

“…However,e xplorations of iodates containing d 8 noble-metal ions (e.g.,A u 3 + or Pd 2 + )a re still limited. [23,24] Within these reported iodates, the squareplanarM O 4 nÀ groups are aligned, they produce strong SHG responses,f or example, RbAu(IO 3 ) 4 [24b] exhibitsaS HG response of 1.33 times that of KTiOPO 4 (KTP). As fort he monovalentm etal gold(III) iodate systems, our group has reporteds ix compounds with the same formula of AAu(IO 3 ) 4 (A = Na,R b, Cs, and Ag), among which the Na and Cs compounds each displays two different types of structures.…”

“…[24b] However,f or K-containing gold iodates,t here is only one compound, namely KAu(IO 3 ) 4 ,r eportedb yt he group of Albrecht-Schmitt in 2007. [23] Despite it crystallizes in the polar space group P1, its SHG property has not been studied.…”

Advances in Study on Structure of Polysaccharide

“…Differential Scanning Calorimetry. In recent years it is in differential thermal analysis technology (thermal analysis differential, DTA) based on the development of a method can be used for the analysis of the advanced structure of polysaccharides [19]. It can not only describe the sample and reference than the temperature, real-time record heat difference variation with temperature, commonly used in evaluation of polymer thermal stability and compatibility and study of polymer material between the interaction [20,21].…”