Dielectric properties of [NH₄][Zn(HCOO)₃] metal formate framework doped with alkali metals.

Recently a metal organic framework [NH₄][Zn(HCOO)₃] has attracted interest of the scientific community. According to Guan-Cheng Xu et al. a paraelectric – ferroelectric phase transition (from P6₃22 to P6₃) was reported at 191 K temperature [1]. Furthermore, MOFs are likely candidates for magnetism, due to possibility to change metal centers, thus having a potential for single crystal multiferroic materials. Our initial studies revelaed a tendency of alkali metals to diffuse into the structure of [NH₄][Zn(HCOO)₃]. Hence, the aim of this work is to investigate the effect on dielectric properties of K and Na impurities in the [NH₄][Zn(HCOO)₃] crystal structure.

In this poster presentation temperature (100-300K) and frequency (10 Hz - 1 GHz) dependences of [NH₄][Zn(HCOO)₃] will be presented. Temperature dependences for [NH₄][Zn(HCOO)₃] at 1 MHz for pure and with different amount of impurities are shown in figure 1. Dielectric results show that with an increase of Na impurities the strength of the dielectric anomaly, due to paraelectric – ferroelectric phase transition at 182 K, decreases. Furthermore with 5 % K impurities this anomaly is less pronounced and shifts to lower temperature from 182 K to 160 K.

Figure 1 Temperature dependence of complex dielectric permittivity of [NH₄][Zn(HCOO)₃] crystal measured along the c-axis.

[1] Xu, Guan-Cheng, et al. "Disorder− order ferroelectric transition in the metal formate framework of [NH4][Zn (HCOO) 3]." Journal of the American Chemical Society 132.28 (2010): 9588-9590.