Ferroelectric Polarization in Nanocrystalline Hydroxyapatite Thin Films on Silicon

Abstract

Hydroxyapatite nanocrystals in natural form are a major component of bone- a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone-density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics.

Компьютерные Исследования Наноструктур Гидроксиапатита, Их Особенности И Свойства

“…It is interesting that, this value is fully in line with the data obtained earlier from cluster models (P ~ 0.005 C/m 2 ) [30]. Corresponding piezoelectric coefficient for this case on the order of dyy = d33 ~ 15.7 pC/N ~ 15.7 pm/V was estimated in [30], which is very close to value d33 ~ 16 pm/V measured in [50], and is twice larger than the value of the experimentally measured in [51] effective piezoelectric coefficient d33eff ~ 8 pm/V, which varies significantly from grain to grain. This deviation was explained in [43] by polar properties variation for different grains: piezoelectric contrast (observed in Ref.…”

“…This deviation was explained in [43] by polar properties variation for different grains: piezoelectric contrast (observed in Ref. [51]) is registered only in some polar grains (ordered monoclinic HAP) and is averaged with other non-polar grain contribution (disordered hexagonal HAP). The resultant contrast turns out to be nearly twice less than the calculated value (corresponding to the case when all the grains are polar).…”

“…It should also be emphasized that the monoclinic ordered phase, P21, could have piezoelectric features in this case [50,51].…”

Hydrophobicity of electron beam modified surface of hydroxyapatite films

“…Typical results of these analyses confirmed that these films were phase pure and nanocrystalline. An earlier investigation has also established the polar nature of these films, which exhibited natural piezo, pyroelectricity [14] and ferroelectrocity [15].…”

Local piezoresponse and polarization switching in nucleobase thymine microcrystals

“…23 teeth, 24 cartilage, 25 diphenylalanine nanotubes, 26 amino acids, 27 hydroxyapatite, 28 and other polar materials including a large number of ferroelectric perovskites. 29,30 In this work, we report on sufficiently strong piezoelectricity and switchable polarization in thymine microcrystals grown from the solution.…”