Crystallographic and thermal expansion properties of rare earth solid solution Er2−xRxMo4O15

Er2−xRxMo4O15 (R = Sm, Nd, Y, Dy) solid solutions were successfully synthesized and their structure characterized by X-ray powder diffraction. All samples are found to crystallize in the monoclinic space group P21/c. Experimental results indicate that amount of Er substitution is restricted in the case of Sm and Nd, with maximal x = 0.6. Thermal expansion properties of Er2−xRxMo4O15 (R = Sm, Nd; x = 0.0, 0.2, 0.6) and Er1.8R0.2Mo4O15 (R = Y, Dy) were studied by high-temperature X-ray diffraction. For the same substitution content, x = 0.2 and through the identical temperature range of 25–500 °C, Y shows the strongest effect on the thermal expansion coefficients (TEC), i.e., TECs of Er1.8R0.2Mo4O15 are 2.65 × 10−5/K, 2.29 × 10−5/K, 2.58 × 10−5/K and 2.43 × 10−5/K for R = Y, Dy, Sm and Nd, respectively, comparing to the TEC of Er2.0Mo4O15 being 1.90 × 10−5/K. Substitution element type and content can affect the TEC of Er2−xRxMo4O15. Bond length analysis suggests that the Er(R)–O is responsible for the overall positive thermal expansion behaviors of these molybdates.

Graphical abstractResults of the Rietveld analysis of the XRD patterns of Er1.8Nd0.2Mo4O15 at 250 °C show that Rp = 4.22%, Rwp = 5.31% and Rexp = 1.95%. The solid line represents the raw data. The + signs represent the calculated profile. Vertical bars indicate the position of Bragg peaks for this phase. The lowest curve is the difference between the observed and calculated patterns. The figure approves that the solid solution Er1.8Nd0.2Mo4O15 has been successfully synthesized and has the same structure with pure R2.0Mo4O15 (R = Er, Dy, Y).Figure optionsDownload full-size imageDownload as PowerPoint slide