Projects / Programmes
Mechanochemical synthesis of complex ceramic oxides
| Code |
Science |
Field |
Subfield |
| 2.09.01 |
Engineering sciences and technologies |
Electronic components and technologies |
Materials for electronic components |
| Code |
Science |
Field |
| T153 |
Technological sciences |
Ceramic materials and powders |
mechanochemical synthsis, piezoelectric ceramic oxides, reaction mechanisms, nanoparticles
Researchers (1)
| no. |
Code |
Name and surname |
Research area |
Role |
Period |
No. of publicationsNo. of publications |
| 1. |
24272 |
PhD Tadej Rojac |
Electronic components and technologies |
Head |
2008 - 2010 |
596 |
Organisations (1)
| no. |
Code |
Research organisation |
City |
Registration number |
No. of publicationsNo. of publications |
| 1. |
0106 |
Jožef Stefan Institute |
Ljubljana |
5051606000 |
90,767 |
Abstract
Piezoelectric materials have established their role in electronic components, as for example in the form of thick films, integrated in microelectromechanical systems (MEMS). The processing of thick films requires high quality powders. Mechanochemical synthesis presents an alternative synthesis of complex ceramic oxide powders. The product is synthesized directly during milling, without the multi-step calcination procedure, which is usually required in the conventional solid-state synthesis.
Due to their complexity, the mechanisms of mechanochemical reactions are presently not well known, especially in the systems where a carbonate reactant is used. For this reason, we focused on the mechanochemical reaction between Na2CO3 and Nb2O5 during the doctoral study. The purpose of the proposed research project is to extend this work to the K2CO3-Nb2O5 and K2CO3-Na2CO3-Nb2O5 systems. The results obtained will enrich the knowledge of the mechanisms of the mechanochemical reactions.
Mechanochemical synthesis allows the preparation of the oxide product with particles in the nanometer range with increased sinterability. Such powders are suitable for thick-film technology, which requires low sintering temperatures in order to avoid the undesired chemical reactions between the active layer and the substrate. So far, the influence of high-energy milling on the sinterability of powders has not been studied sufficiently. The second part of the research project will be a systematic study of the morphology of differently milled powders and its influence on the sinterability as well as on the final density of ceramics. The purpose is to evaluate the problem of particles agglomeration during milling with the aim to obtain dense ceramics and thick films at lower temperatures.
The results of the research project will contribute to the basic understanding of the process as well as to progress of the synthesis method with the aim to prepare ceramics and thick films with improved piezoelectric properties.
Significance for science
Mechanochemical synthesis has recently become a promising synthesis route for the preparation of various complex ceramic oxides. One of the major obstacles that has to be overcomed in the future is a poor knowledge of the basic mechanisms of mechanochemical reactions for which limited literature data exist, especially on systems where a carbonate compound is involved.
The results of the research project give an insight into the basic mechanisms and characteristics of mechanochemical synthesis and are consequently extremely important for science. The key factor that leaded to these scientific cognitions was a careful plan of the research work, which was based on the use of selected analytical methods and quantitative approach. The study included reactions in several systems, which allowed making general observations and through this it represents an original contribution to science.
The comparison of the course of reactions in the Na2CO3–Nb2O5 and K2CO3–Nb2O5 systems revealed a common mechanism, which is characterized by the formation of a carbonato complex. The stability of this complex is much higher in the system with potassium. In this system the crystallization products after prolonged milling time (350 hours) and high ball-impact energy (300 mJ), when the complex partially decomposes, are KNbO3 together with other niobate phases with molar ratio K/Nb < 1. The results related to high-energy milling of NaNbO3 and KNbO3 showed that KNbO3 is unstable under high-energy impacts and decomposes partially to other niobate phases, which could explain the difficulties related to the synthesis of this compound. The decomposition of KNbO3 and its instability upon milling is important from the scientific viewpoint as it offers a possible explanation for mechanochemical reactions in other systems, where final product are difficult or even impossible to be formed directly by milling.
The results of the systematic study of the reactions in Na2CO3–X2O5 (X = V, Nb, Ta) systems leaded to important and new scientific revelations related to the mechanism of reactions between a carbonate and oxide compound, for which there are no literature data. The reactions are characterized by an acid-base interaction between dissimilar particles that is driven by high-energy impacts. Thus, the higher the acid-base potential between Na2CO3 and transition metal oxide (V2O5, Nb2O5, Ta2O5), the faster the reaction, from the formation of carbonato complex to its decomposition and final crystallization of products. The results represent a completely new contribution to science and enrich the understanding of basic characteristics of mechanochemical reactions.
One of the key scientific questions, treated insufficiently in the literature, is the origin of the high homogeneity of the mechanochemically activated powders. Within the research project we elucidated this point by studying the mechanochemcial activation in the K2CO3–Na2CO3–Li2C2O4– Nb2O5–Ta2O5 system, where the goal was to prepare (K,Na,Li)(Nb,Ta)O3 (KNLNT) ceramics. We showed that during activation a carbonato complex is formed, in which the carbonate ions are coordinated to Nb and Ta as central cations. The origin of the high homogeneity of the activated powder lies in the formation of this new amorphous compound, which is crucial to obtain KNLNT ceramics with high homogeneity. As a matter of fact, poorly homogeneous KNLNT ceramics was obtained if the initial powder mixture was activated in the “friction” milling regime, during which we did not observe the formation of the carbonato complex.
Significance for the country
Presently, we are partaking in a rapid development of materials for electronics, including piezoelectric materials, which can be found in a form of thick films integrated into micro-electro-mechanical systems (MEMS). Layered structures necessitate in the first place high-quality powders. One of the possibilities to prepare nanopowders is mechanochemical synthesis, which is based on a simple dry milling technique and is potentially applicable to the industrial scale.
In the framework of the research project we evaluated the possibility to utilize the mechanochemically processed powders in thick-film technology. The results of the project show that using mechanochemical synthesis homogeneous and fine powders can be obtained without undesidarable secondary phases and with a low amount of impurities, originating from the milling process. The powders based on alkaline niobates (tantalates), which were prepared within the project, are suitable for thick-film technology.
One of the goals of the project was to replace lead-based materials, such as Pb(Zr,Ti)O3, with environmentally friendly materials. During the project we successfully synthesized homogeneous powders of lead-free compositions. Thick films prepared from these powders showed good piezoelectric properties. The results of the project are useful for the company “HYB proizvodnja hibridnih vezij, d.o.o.«, which is involved in the research, production and trade of pressure sensors and hybrid thick-film electronic micro-circuits. The project contributed to the development of the scientific recognition of Slovenia. Based on the acquired knowledge, it created a platform for the introduction of new, environmentally friendly materials for electronics, which is in line with European directives.
Most important scientific results
Annual report
2008,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2008,
final report,
complete report on dLib.si
