X-Ray Diffraction Study on the Incommensurate-Commensurate Phase Transitions in {N(CH3)4}2CoCl4

By means of X-ray diffraction study two incommensurate phases were found in {N(CH 3 ) 4 } 2 CoCl 4 in the temperature ranges of 20.6∼8.0°C and 6.3∼4.5°C. As the temperature decreases, the modulation wave vector q 0 decreases from about 0.42 c * at 20°C to the commensurate value of 2/5 c * without a recognizable jump at 8.0°C. Between 8.0 and 6.3°C, it stays at 2/5 c * and below 6.3°C it decreases from 2/5 c * to about 0.39 c * at 4.5°C and then jumps to the commensurate value of 1/3 c * . Between 4.5 and –81°C (monoclinic phase) it stays at 1/3 c * .