Nature of ferroelectricity in nonperovskite semiconductors like ZnO:Li

Abstract

We show that in nontypical ferroelectric substances (having nonperovskite crystalline structure and hence no soft phonon mode) such as ZnO:Li, Be, Mg, the ferroelectricity might appear due to indirect interaction of dipoles, formed by Li, Be, or Mg off-center impurities, via free charge carriers. Our estimations show that the typical semiconducting concentration of the carriers like 1017 cm−3 suffices for effect to occur. We have also shown that the properties of impurity-generated ferroelectricity depend on the difference in the ionic radii of the impurity and host lattice ion as well as on their concentrations. Namely, the growing amount of Li and Be promotes ferroelectricity, while the same for Mg inhibits it. Our calculations of spontaneous polarization and ferroelectric phase transition temperature in the above nontypical ferroelectrics as the functions of concentrations of impurity dipoles and carriers capture well the main peculiarities of all available experimental data.

Carrier concentration dependence of ferroelectric transition in multiferroic Li doped and Li-Co co-doped ZnO nanoparticles

“…26 The formation of the zinc vacancy, each generating two holes, more than offsets the electron donated by the Li interstitial. Here, we note that the hole concentrations that we have determined in our samples lie in the range 2.4 Â 10 17 /cc-7.3 Â 10 17 /cc consistent with the discussion 18 where such levels of hole concentrations have been shown as being sufficient to generate the indirect coupling of the electric dipole moments.…”

“…17 The interaction between separated dipoles via an indirect interaction mediated by the free carriers (holes) has been proposed. [18][19][20][21] Another suggested mechanism is that of the so-called pseudo-ferroelectric behavior 22 arising from the effects of an intrinsic bias field in such materials. There are however no reports on the dielectric behavior of Li/Co doped ZnO nanoparticles where finite size effects are also expected to play a significant role in the electronic and structural properties.…”

Ba-DOPED ZnO MATERIALS: A DFT SIMULATION TO INVESTIGATE THE DOPING EFFECT ON FERROELECTRICITY

“…[13][14][15][16][17][18] However, the production process of such devices is hampered due to the difficulty of interface between perovskite-type structure and Si substrate. 13,[19][20][21] ZnO and Ba-doped ZnO can be easily adjusted to this substrate because of similar structures; such as, tetrahedral sites, hexagonal group and lattice parameters. Based on our theoretical results, the ZnO:Ba at 87.5% is a potential alternative to replace perovskite-type materials in ferroelectric devices, for instance, Random Access Memory (RAM), flash-type memories or flash-drives; nevertheless, the structural instability forecasted can be a great challenge to synthesis methods.…”

“…[13][14][15][16][17][18] However, the application of these materials is difficult and significantly delayed due to hard adjustment between the semiconductor structure lattice parameters and the substrate, mainly on Si substrates. 13,[19][20][21] Besides, the perovskite nanostructure properties can be drastically different from its bulk properties; 6 thus, simple oxide semiconductors are presented as a viable alternative to replace the perovskite materials. 3,6,21,22 For many years, the wurtzite zinc oxide (ZnO) has attracted interest due to its unique electronic, optical and piezoelectric properties.…”

“…40 Nowadays, theoretical and experimental studies on doped ZnO materials have been performed to propose materials which might be viable alternatives to replace the perovskite materials. 6,9,10,12,19,20,29,[41][42][43] Thus, the aim of this study was to perform computational simulations based on DFT/B3LYP to evaluate the effect of low and large Ba doping on ZnO due to its great potential to replace perovskite-type materials in ferroelectric and opto-electronic devices.…”