How Can Surface-Crystallized Glass-Ceramics Be Piezoelectric?

Abstract

The surface crystallization of non-ferroelectric, polar crystals from a glass often leads to piezoelectric surface layers. The surface layer not only shows a crystallographic orientation preference (texture) but also prefers one polarity during crystal growth. This cannot be explained by the common periodic bond chain theory or Bravais–Friedel–Donnay–Harker law. For the most frequently studied polar crystals in glass-ceramics, fresnoites of the general composition (Ba/Sr)2Ti­(Si/Ge)2O7 or lithium disilicate (Li2Si2O7), the dipoles are, respectively, aligned antiparallel or parallel to the dominant growth direction after crystallization. Hence, the polarity of the crystals cannot be the decisive factor for texture development. Taking the structure of the respective unit cells into account shows that these crystals grow with the corners of coordination polyhedra oriented toward the bulk. This is in agreement with the coordination polyhedra rule, according to which crystal growth along the direction of polyhedral corners should be preferred while the edges show the second-highest growth rate. Furthermore, the planes parallel to the face of the coordination polyhedron undergo the slowest growth.

A new perspective for nucleation and nanocrystallization from interfacial energy and nanoscale composition fluctuations in glasses

“…Fresnoite Ba 2 TiSi 2 O 8 (BTS) crystals with an anisotropic layered structure exhibit excellent piezoelectric and second‐order nonlinear optical properties, and many studies on crystallization behaviors in BaO–TiO 2 –SiO 2 ‐based glasses and the performance of glass‐ceramics consisting of BTS crystals have been carried out 8,38,86,128–133 . In particular, as reported by Cabral et al., 38,88 a stoichiometric BTS glass with a composition of 40BaO–20TiO 2 –40SiO 2 (mol%) shows a prominent homogeneous bulk nucleation with an extremely high nucleation rate of I max ∼ 10 17 /m 3 ·s among SiO 2 ‐based glasses/SCLs.…”

“…9 Recently, as the mechanism for the orientation of polar crystals such as lithium disilicate Li 2 Si 2 O 7 and fresnoite-type Ba 2 TiGe 2 O 8 observed at the surface of crystallized glasses, the coordination polyhedral rule 85 has been proposed to work well. 86 In this model, the crystal growth along the direction of polyhedral corners should be preferred while edges show the second highest growth rate. Further studies on the origin and mechanism for the orientation of crystals in crystallized glasses might be required.…”

“…Considering the concept of surface energy, it is expected that the (001) plane (i.e., the c ‐plane) has a lower surface energy compared with the (100) (i.e., the a ‐plane) and (010) (i.e., the b ‐plane) planes, that is, γ sur ( c ‐plane) < γ sur ( a ‐plane), consequently suggesting that the preferential crystal growth direction of β‐BBO is the c ‐axis, that is, the c ‐axis orientation 9 . Recently, as the mechanism for the orientation of polar crystals such as lithium disilicate Li 2 Si 2 O 7 and fresnoite‐type Ba 2 TiGe 2 O 8 observed at the surface of crystallized glasses, the coordination polyhedral rule 85 has been proposed to work well 86 . In this model, the crystal growth along the direction of polyhedral corners should be preferred while edges show the second highest growth rate.…”

An EBSD Study on Crystallization of CaO-MgO-Al2O3-SiO2 (CMAS) Glass

“…Besides all these, in recent years, since the orientation of the formed crystals is a decisive parameter for some properties of glass-ceramics, whether the crystals are oriented while growing has become a considerable research topic [15][16][17]. Especially in non-ferroelectric glass-ceramics, crystal orientation can lead to forming a piezoelectric and/or pyroelectric surface layer [15,17,18]. Surface crystallization is a highly preferred method of obtaining glass-ceramics where the growth orientation of crystals is essential [15][16][17].…”

“…Especially in non-ferroelectric glass-ceramics, crystal orientation can lead to forming a piezoelectric and/or pyroelectric surface layer [15,17,18]. Surface crystallization is a highly preferred method of obtaining glass-ceramics where the growth orientation of crystals is essential [15][16][17]. During surface crystallization, crystals grow into the inner region of the parent glass after nucleation occurs on or near the surface [19].…”