Heat Capacity and Thermodynamic Functions of Sr(La1-xLnx)2WO7 Compounds Doped with Samarium and Europium

D T Sadyrbekov,M R Bissengaliyeva,N S Bekturganov,S T Taimassova,D B Gogol

doi:10.18321/ectj1031

Abstract

Samples based on strontium, lanthanum and tungsten with the general formula of Sr(La1-xLnx)2WO7 doped with samarium and europium at 1 and 3 at.% were synthesized by the solid-phase method at temperatures up to 1200 °C. The crystal structure of the samples was confirmed by X-ray powder diffraction. A full-profile refinement of the structure of compounds related to monoclinic syngony with the space group P1121/b was performed. The admixture phase is a compound of the Sr3Ln2W2O12 type with a trigonal system and space group R3-C. Based on the results of structure refinement, the ratio of the main compound and the admixture phase in the samples was determined to introduce corrections during measurements. Using adiabatic calorimetry we measured the heat capacity of the samples and found the thermodynamic functions of main compounds over the range of 5‒320 K. Anomalies were detected in the heat capacity of the samples below 15 K, and we calculated the excess and lattice heat capacity for these anomalies by means of linearization methods.

Highlights

Rare-earth metals are used in the production of optical materials for various purposes
Due to the transitions 4f–4f or 5d–4f, they are widely used as luminophores, etc. [1]
Strontium carbonate SrCO3, tungsten oxide (VI) WO3, and rare-earth oxides of lanthanum La2O3, samarium Sm2O3, and europium Eu2O3 of the qualification “chemically pure” were used as starting materials for synthesizing samples designated as SrLa(Sm)-W and Sr-La-(Eu)-W

Summary

Introduction

Rare-earth metals are used in the production of optical materials for various purposes. In reference [3] synthesized luminophores based on strontium tungstate doped with Eu3+ and. The phase structure, morphology, and luminescent properties are described. The advantage of europium compared to other dopants is its wide charge pass band in the region. The research into the luminescent properties of SrLa2WO7 doped with europium [6,7,8] is presented in the literature, while no description of thermodynamic characteristics is available there. Low-temperature studies of the heat capacity were carried out by adiabatic calorimetry and the main thermodynamic functions were determined. Abnormal deviations from the usual course of the heat capacity curve were detected, indicating the possible presence of the second-order phase transitions. The study results on the structural parameters of the synthesized samples are presented

Synthesis

X-ray study

Adiabatic calorimetry

Results and discussion

Conclusion