Crystal Structure and Site Preference of Ba-Doped α-Tricalcium Phosphate (Ca_1-xBa_x)₃(PO₄)₂through High-Resolution Synchrotron Powder Diffraction (x= 0.05 to 0.15)

Abstract

The single phase of barium-substituted alpha tricalcium phosphate (Ba-α-TCP) (Ca1- x Ba x )3(PO4)2 (x = 0.05, 0.10, and 0.15) has been prepared by solid-state reactions. The crystal structure of the Ba-α-TCP powders has been investigated by high-resolution synchrotron powder diffraction and the Rietveld method. Diffraction data were successfully analyzed by the single phase Ba-α-TCP (space group P21/a). Unit-cell parameters a, b, c, and β increase with increasing Ba content. Most of the Ba atoms are located at three crystallographic sites among the eighteen cation sites in the α-(Ca1- x Ba x )3(PO4)2 (x = 0.05, 0.10, and 0.15). The refined positional parameters and occupancy factors of the preference sites for Ba substitutions were Ca17: (0.0909(6), 0.4167(2), 0.7823(5)) g(Ba) = 0.72(2); Ca11: (0.4068(6), 0.2506(2), 0.2199(5)) g(Ba) = 0.67(1); Ca5: (0.0983(6), 0.0837(2), 0.7857(5)) g(Ba) = 0.65(1) in the α-(Ca0.85Ba0.15)3(PO4)2. Here, g(Ba) is the occupancy factor of Ba atoms. These sites have relatively smaller bond valence sums, indicating the preference sites for the larger-sized Ba substitutions.

First principle study of structural, phase stabilization and oxygen-ion diffusion properties of β-La2−xLxMo2O9 (L=Gd, Sm, Nd and Bi) and β-La2Mo2−yMyO9 (M=Cr, W)

“…This suggested that the BVS values in undoped system could be used as an indicator for the site preference of dopant cations: the dopant cations with relatively large ionic radius prefer to sites with smaller BVS values; while small dopant cations preferentially occupy crystallographic sites with larger BVS values. This correlation of the site preference of doping atom and BVS values is similar to that reported by Yashima and Kawaike [32]. It should be noted that the case of Bi 3+ substitution on La 3+ is not consistent with this regulation.…”

“…Hence they are usually used to explain some perplexing problem of stability of structure. For example, Harrington [32]. Our third goal of this paper is to validate the correlation of the site preference of doping atom and BVS in β-La 2 Mo 2 O 9 based on first principle results.…”

Thermally Induced Crystallization and Phase Evolution of Amorphous Calcium Phosphate Substituted with Divalent Cations Having Different Sizes

“…However, the evolution of the XRD patterns corresponds to the internal structural changes of α-TCP, but not to the formation of secondary crystal phases. For comparison, the XRD pattern of 10 mol % Ba-doped α-TCP reported by Yashima and Kawaike was added. These authors performed a detailed study on the crystal structure and the site preference of the Ba-doped α-TCP through high-resolution synchrotron powder diffraction.…”

Synthesis, structure and optical properties of europium doped calcium barium phosphate – a novel phosphor for solid-state lighting

“…7 The CaO-BaO-P 2 O 5 phase diagram is well understood and includes many complex phases such as (Ca,Ba) 2 P 2 O 7 , Ca 2 Ba(PO 4 ) 2 , (Ca,Ba) 3 (PO 4 ) 2 , Ca 10 (PO 4 ) 6 O and Ca 4 (PO 4 ) 2 O. [8][9][10] However the system has been little explored for phosphor applications in combination with blue LEDs. Lagos reported the behavior of (Ca,Ba) 2 P 2 O 7 :Eu 2+ as a blue phosphor and (Ca,Ba) 3 (PO 4 ) 2 :Eu 2+ as a yellow phosphor for UV excitation, but these are not alternatives to YAG:Ce 3+ since they are poorly matched to blue LEDs.…”