Linear spin wave theory provides the leading term in the calculation of the excitation spectra of long-range ordered magnetic systems as a function of 1/root S. This term is acquired using the Holstein-Primakoff approximation of the spin operator and valid for small dS fluctuations of the ordered moment. We propose an algorithm that allows magnetic ground states with general moment directions and single-Q incommensurate ordering wave vector using a local coordinate transformation for every spin and a rotating coordinate transformation for the incommensurability. Finally we show, how our model can determine the spin wave spectrum of the magnetic C-site langasites with incommensurate order.

https://iopscience.iop.org/article/10.1088/0953-8984/27/16/166002/pdf

Linear spin wave theory for single-Q incommensurate magnetic structures

Surface acoustic wave (SAW) technology provides a sensitive platform for sensing chemicals in gaseous and fluidic states with the inherent advantages of passive and wireless operation. In this review, we provide a general overview on the fundamental aspects and some major advances of Rayleigh wave-based SAW sensors in sensing chemicals in a gaseous phase. In particular, we review the progress in general understanding of the SAW chemical sensing mechanism, optimization of the sensor characteristics, and the development of the sensors operational at different conditions. Based on previous publications, we suggest some appropriate sensing approaches for particular applications and identify new opportunities and needs for additional research in this area moving into the future.

SAW Sensors for Chemical Vapors and Gases.

In the last few years, there has been tremendous effort to develop lead-free ferroelectric ceramics with high piezoelectric properties by various doping and alloying routes. Several material systems have been explored, however, no prominent alternative to the versatile lead zirconate titanate (PZT) system has been found yet. Despite the achieved improvement in piezoelectric properties, there are problems in the synthesis, processing and poling of the sintered ceramics. Various processing techniques including microwave, hydrothermal, sol–gel, Pechini and spark plasma sintering have been used to overcome the drawbacks related to synthesis issues. In this paper, an attempt is made to review recent developments on lead-free piezo materials emphasizing their preparation, structure–property relations, and consequent physical properties. In this context, both compositional and structural engineering approaches to achieve acceptable piezoelectric properties in lead-free materials are discussed. Piezoelectric properties of the most promising lead-free compositions/families including titanates, alkaline niobates and bismuth perovskites and their solid solutions, along with non-perovskites such as bismuth layer-structured ferroelectrics are reviewed in detail. A brief coverage of the recent developments in the area of piezoelectric energy harvesting is also encompassed.

https://www.worldscientific.com/doi/pdf/10.1142/S2010135X13300028

Lead-free piezoelectrics: Current status and perspectives

The luminescence induced by elastic deformation of solids, called the phenomenon of elastico-mechanoluminescence (EML), is observed in several materials. For applied pressure in the range of 17 MPa, certain crystals emit intense EML, which can be seen in day light with naked eye. In the present paper, we explore that, as the piezoelectric constant near the photo-generated electric dipoles formed by trapping of charge carriers in crystals is several times higher as compared to that at normal sites, the piezoelectrically induced detrapping of charge carriers and EML emission may take place for less value of the pressure applied onto the crystals.

Strong luminescence induced by elastic deformation of piezoelectric crystals

Impulsive excitation of mechanoluminescence in SrAl2O4:Eu, Dy phosphors prepared by solid state reaction technique in reduction atmosphere

Langasite family crystals ( R 3 Ga 5 SiO 14, R= rare earth) are expected as the new piezoelectric material for SAW filter. La 3 Ga 5 SiO 14 has the largest piezoelectric modulus in these crystals. It is reported that the piezoelectric properties of these crystals improved with the increase of the ionic radius of R . In this work, we clarified the crystal structures of three kinds of langsite family crystals ( R =La, Pr and Nd) by X-ray diffraction analysis. We investigated the differences among these crystal structures and clarified the reason why the piezoelectric properties improved with the increase of the ionic radius of R on the basis of these structural differences.

Mechanism of the piezoelectricity of langasite based on the crystal structures

Piezoelectric langasite crystals have superior properties such as high temperature performance and high quality Q and can be applied in combustion pressure sensors and surface acoustic wave (SAW) filters. Crystal growth, crystal structure and properties of langasite group are reviewed, and the mechanism of piezoelectricity of langasite is presented based on the crystal structure and deformation under high pressure. Finally, for the discovery of new piezoelectric materials, this paper presents the role of the framework, and recommends the search of framework crystal structure, because the characteristic of the mechanism exists on the framework of the crystal structure.

Mechanism of Piezoelectricity for Langasite Based on the Framework Crystal Structure

As langasite compounds with piezoelectric properties exhibit no phase transition up to the melting point of 1,400-, many high temperature applications are expected for the SAW filter, temperature sensor, pressure sensor, and so on, based on the digital transformation of wider bandwidth and higher-bit rates. It has a larger electromechanical coupling factor compared to quartz and also nearly the same temperature stability as quartz. The (LGS) crystal with the -type crystal structure was synthesized and the crystal structure was analyzed by Mill et al. It is also an important feature that the growth of the single crystal is easy. In the case of three-element compounds such as (R

/pdf/crystal-structure-and-piezoelectric-properties-of-four-l85w9d69z7.pdf

Crystal Structure and Piezoelectric Properties of Four Component Langasite A 3 B Ga 3 Si 2 O 14 (A = Ca or Sr, B = Ta or Nb)

Piezoelectric properties of langasite group based on the ionic size of cation

/pdf/investigation-on-the-structural-differences-among-langasites-1cb7bsvmr6.pdf

Tsuyoshi Iwataki

Papers

Mechanism of the piezoelectricity of langasite based on the crystal structures

Mechanism of Piezoelectricity for Langasite Based on the Framework Crystal Structure

Crystal Structure and Piezoelectric Properties of Four Component Langasite A 3 B Ga 3 Si 2 O 14 (A = Ca or Sr, B = Ta or Nb)

Piezoelectric properties of langasite group based on the ionic size of cation

Investigation on the structural differences among langasites by single-crystal X-ray structure analysis