A very promising piezoelectric property of thin films. I: Monoclinic–trigonal phase transition

Particular structural defects in Ta2O5 from crystallisation of amorphous thin films in O2–H2O atmosphere

“…The origin of structural defects within mL-Ta 2 O 5 phases of monoclinic structures as observed in previous works [29,16], is here shown to be the result of a reaction with H 2 O gas through the crystallisation of amorphous thin films deposited by i-MOCVD. These structural defects are linear and correspond to alignments of Ta 5+ and O 2 vacancies (or Ta 5+ only) along a [001] direction and assembled at domain boundaries in rotations of AE2p/3 or AE2p/6 about [001].…”

“…6 The objective of these experiments was twofold: to examine (i) if structural defects incorporate alkaline cations (instead of H + ) whose concentration can be measured and (ii) if Ta 2 O 5 transforms into a phase (Na x K 1Àx ) 2 Ta 4 O 11 of trigonal structure. Such a trigonal phase, whose atomic structure is similar to that of the natural natrotantite mineral Na 2 Ta 4 O 11 [27,28], has been found to exhibit interesting properties of piezoelectricity [16,29]. Through different atomic substitutions (e.g., Ta 5+ by Nb 5+ , Na + by Cu + or Ag + ) it exhibits also photo-catalytic [30,31] ferroelectric and non-linear optical properties [32][33][34].…”

“…Their indexing was made after identifying by TEM and XEDS a trigonal phase (a R % 12.7 Å , a % 28.2°in the rhombohedral cell system) of composition close to (Na x K 1Àx ) 2 Ta 4 O 11 (x % 0:8). The small number of reflection observed for this phase is due to its texture resulting of its crystallographic orientation relationships with monoclinic mL-Ta 2 O 5 phases [16,29], i.e. ½111 R k½001 o ; ½ 12 1 R k½010 o and ½10 1 R k½100 o , where subscripts R and o stand for the rhombohedral cell and the orthorhombic sub-cell of Lehovec [23].…”

The effect of Ta doping in polycrystalline TiOx and the associated thin film transistor properties

“…Furthermore, extra electrons can be easily generated by increasing the density of Ta 5þ ions whereas the Ti 4þ ions are relatively suppressed. 11,[14][15][16] In the present work, the electrical performance of Ta-doped TiO x TFTs is evaluated, and the relevant material properties such as crystallinity, electronic structures, and chemical states are also analyzed.…”

Propiedades piezoeléctricas del Pentóxido de Niobio y Pentóxido de Tantalio

“…Sin embargo, no todas las fases de estos compuestos presentan propiedades piezoeléctricas, ya que de acuerdo con la simetría puntual asociada a cada una de las fases, se puede identificar que solamente una parte de estas, con grupo puntual no-centro simétrico, presentan estas propiedades, entre las que podemos destacar P y Z para Nb2O5 [3], [5], Z y β (modelo Ramprasad) para Ta2O5 [6], [7]. Debido a la gran importancia de la piezoelectricidad a nivel industrial, estudios experimentales en películas delgadas de Ta2O5 usando técnicas de pulverización, reportaron que las películas delgadas de Ta2O5 con estructura monoclínica pertenecientes al grupo puntual m, exhiben propiedades piezoeléctricas comparables a ZnO [2], [8], [9], [10].…”