A Mossbauer study of La1-xEuxB6 compounds synthesized at high pressure andtemperature

A series of hexaborides La1-xEuxB6 (x=0.0-1.0) were synthesized under a pre ssure of 3.5 GPa and at a temperature of 1600 degreesC using La2O3, Eu2O3 a nd amorphous boron as the starting materials. The products were characteriz ed by X-ray Diffraction (XRD) and Mossbauer spectroscopy. XRD data analysis shows that all samples crystallize in a cubic CsCl-type structure, and the cell volume increases with x. Room temperature Eu-151 Mossbauer measuremen ts reveal that Eu ions in all samples are in the divalent state, except for the x=1.0 sample where a small amount of Eu3+ ions was detected. The quadr upole splitting of the Eu2+ ions is positive. Eu ions were reduced from tri valent to divalent during the high-pressure and -temperature processes. The isomer shifts of the Eu2+ ions are all smaller than -12.5 mm/s, suggesting that there is no valence fluctuation in the samples. The hexaborides doped by divalent Eu are not metallic.