Phase separation, effects of magnetic field and high pressure on charge   ordering in y-Na0.5CoO2
  Transmission electron microscopy observations reveal the presence of complex superstructures and remarkable phase separation in association with Na-ordering phenomenon in y-Na0.5CoO2. Resistivity and magnetization measurements indicate that three phase transitions at the temperatures of 25 K, 53 K and 90 K respectively appear commonly in y-Na0.5CoO2 samples. Under a high pressure up to 10 Kbar, the low-temperature transport properties show certain changes below the charge order transition; under an applied magnetic field of 7 Tesla, phase transitions at around 25 K and 53 K, proposed fundamentally in connection with alternations of magnetic structure and charge ordering maintain almost unchanged. 
H.X. Yang, Y.G. Shi, C.J. Nie, D. Wu, L.X. Yang, C. Dong, H.C. Yu,   H.R. Zhang, C.Q. Jin, and J.Q. Li