[Pb_0.95(La_1−𝑦Bi_𝑦)_0.05][Zr_0.53Ti_0.47]O₃ (PLBZT) ferroelectric thin films have been synthesized on indium tin oxide (ITO)-coated glass by sol–gel processing. PLBZT thin films were annealed at a relatively low temperature of 550 °C in oxygen ambient. Effects of Bi doping on structure, dielectric and ferroelectric properties of PLBZT were investigated. Bi doping is useful in crystallization of PLBZT films and promoting grain growth. When the Bi-doping content 𝑦 is not more than 0.4, an obvious improvement in dielectric properties and leakage current of PLBZT was confirmed. However, when the Bi-doping content is more than 0.6, the pyrochlore phase appears and the remnant polarization 𝑃_r of PLBZT thin films is smaller than that of (Pb_1−𝑥La_𝑥)(Zr_1−𝑦 Ti_𝑦)O₃ (PLZT) thin films without Bi doping. PLBZT thin films with excessive Bi-doping content are easier to fatigue than PLZT thin films.

A novel (1−𝑥)Ba_0.7Bi_0.3Fe_0.9Sn_0.1O₃-𝑥BaCo$_{0.02}^{II}$ Co$_{0.04}^{III}$Bi_0.94O₃ (0.2 ≤ 𝑥 ≤ 0.9) negative temperature coefficient (NTC) thick film thermistors with high thermistor constant was prepared by screen printing. The values of room-temperature resistivity, thermistor constant and activation energy of the thick film thermistors, increasing with the addition of Ba_0.7Bi_0.3Fe_0.9Sn_0.1O₃, are in the range of 35.5 𝛺cm-1.34 M𝛺 cm, 2067–6139 K and 0.177-0.527 eV, respectively. This means that the electrical properties of the thick films are adjustable at a wide range, depending on the compositions. Impedance analysis shows that the magnitude of thick film bulk resistance is mainly attributed to the contribution of grain boundary.

Lead-free piezoelectric ceramics $(1−x)$[0.95(K$_{0.5}$Na$_{0.5}$)NbO$_3$–0.05LiSbO$_3$]–$x$BiFe$_{0.8}$Co$_{0.2}$O$_{3}$(KNN–LS–$x$BFC) were prepared by a conventional sintering technique. The effect of BFC content on the structure, piezoelectricand electrical properties of KNN–LS ceramics was investigated. The results reveal that the BFC is effective in promoting the sinterability and the electrical properties of the ceramics sintering at low temperature of 1030$^{\circ}$C. Theceramics show a single perovskite structure, in which the tetragonal phase decreases while the orthorhombic phase increases with the increase of $x$. The more the BFC content is, the smaller and homogeneous grains were formed.With the increase of $x$, the $d_{33}$ and the $k_p$ increase to a maximum value and then slightly decrease, but the $Q_m$ increases continuously. As BFC content increases, the Curie temperature $T_c$ and remnant polarization $P_r$ decrease, but the diffusivity of phase transition in KNN–LS ceramics will intensify and the coercive field $E_c$ fluctuate between 1.16 and 1.51 kV mm$^{−1}$. The samples with $x =0.004$ exhibit optimum electrical properties at room temperature ($d_{33} = 268 pC$ N$^{−1}$, $k_p =52$%, $\epsilon_r = 1366$, $\tan \delta =2.11$%, $T_c = 325^{\circ}$C, $P_r = 20.4$ $\mu$C cm$^{−2}$, $E_c =1.16$ kV mm$^{−1}$).

Ag/La$_{1−x}$Zn$_x$MnO$_3$/p$^+$-Si devices with different Zn doping contents were fabricated through sol–gel method. The effects of Zn doping concentration on the microstructure of La$_{1−x}$Zn$_x$MnO$_3$ films, as well as on the resistance switching behaviour and endurance characteristics of Ag/La$_{1−x}$Zn$_x$MnO$_3$/p$^{+}$-Si were investigated. After annealing at 600$^{\circ}$C for 1~h, the La$_{1−x}$Zn$_x$MnO$_3$ ($x = 0.1$, 0.2, 0.3, 0.4, 0.5) are amorphous and have bipolar resistance characteristics, with RHRS/RLRS ratios $>$103. However, the endurance characteristics show considerable differences; $x = 0.3$ shows the best endurance characteristics in more than 1000 switching cycles. The conduction mechanism of the Ag/La$_{1−x}$Zn$_x$MnO$_3$/p$^{+}$-Si is the Schottky emission mode at high resistance state. However, the conduction mechanism at low resistance state varies with Zn doping concentration. The dominant mechanism at $x = 0.1$ is filamentary conduction mechanism, whereas that at $x \ge 0.2$ is space-charge-limited current conduction.

It is well known that domains and crystal structure control the physical properties of ferroelectrics. The ex-situelectric field-dependent structural study, carried out in unpoled/poled crushed powder and bulk samples for (Li$_{0.5}$Nd$_{0.5}$)$^{2+}$ modified 0.95Bi$_{0.5}$Na$_{0.5}$TiO$_3$−0.05BaTiO$_3$ solid solution, established a correlation between domain configuration andcrystal structure variation. Under applying electric field, the smeared ferroelectric phase structure due to coherence diffractioneffect of nanodomains reappeared due to obsolescent coherence effect associated with the field-induced ordered nanodomains.The macroscopic characterizing techniques of domain configuration such as dielectric constant spectroscopy and X-raydiffraction measurement can provide a basis for understanding the correlation between domains configuration and crystalstructure in ferroelectric ceramics.

The Sr$_{0.88}$Bi$_{0.12}TiO$_3$/SrTi$_{0.92}$Mg$_{0.08}$O$_3$ (SBTO/STMO) heterostructure films were prepared on p$^+$-Si substratesby sol–gel spin-coating technique, and the films had good crystallinity and uniform grain distribution. The heterostructure films with a structure of Ag/SBTO/STMO/p$^+$-Si exhibited a bipolar, remarkable resistance-switching characteristic, and $R_{\rm HRS}/R_{\rm LRS} \sim 10^4$. More importantly, the heterostructure films showed rectifying characteristic in the low resistance state (LRS), and the rectification ratio can reach 10$^2$ at $\pm$1 V. The dominant resistive-switching conduction mechanism of high resistance state (HRS) was Ohmic behaviour, and the LRS changed to space charge-limited current(SCLC).

SrTiO$_3$ and Bi-doped SrTiO$_3$ films were fabricated with different device structures using the sol–gel method for non-volatile memory applications, and their resistance-switching behaviour, endurance and retention characteristics were investigated. SrTiO$_3$ and Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films grown on Si or Pt have the same phase structure, morphologies and grain size; however, the grain size of the Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films grown on Si is slightly larger than those of the SrTiO$_3$ films grown on Si and the Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films grown on Pt. The SrTiO$_3$ or Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films grown on Si or Pt all exhibitbipolar resistive-switching behaviour and follow the same conductive mechanism; however, the Ag/Sr$_{0.92}$Bi$_{0.08}$TiO$_3$/Si device possesses the highest $R_{\rm HRS}/R_{\rm LRS}$ of 10$^5$ and the best endurance and retention characteristics. The doping of Bi is conducive to enhance the $R_{\rm HRS}/R_{\rm LRS}$ of the SrTiO$_3$ films; meanwhile, the Si substrates help improve the endurance and retention characteristics of the Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films.

Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ ($x = 0.025–0.125$) thin films were synthesized by applying a sol–gel method on fluorine-doped tin oxide substrates. The influence of Ni doping concentration on the structure, leakage current, ferroelectric, magnetic and optical properties of Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ thin films was investigated. Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ thin films are polycrystalline films that present a single perovskite structure without any impurity phase when the Ni doping concentration is below 0.1 and present a Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ phase when the Ni doping concentration is above 0.1. The grain size of the films and their holes gradually decrease with an increase in the Ni doping amount. The saturation magnetization of Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ thin films increases with Ni content.However, appropriate Ni doping concentration can decrease the leakage current and enhance the ferroelectric polarization and optical transmittance of the films. Meanwhile, the absorption edge has a slight red shift. Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ thin films possess better combination properties at a leakage current density of $4.27 \times 10^{−9}$ A cm$^{−2}$, ferroelectric polarization of 28.58 $\mu$C cm$^{−2}$, saturation magnetization of 2.08 emu cm$^{−3}$ and transmittance of over 85% when the Ni doping concentration, $x$ is 0.05.

The complex ions (Mn$_{1/3}$Nb$_{2/3}$)$^{4+}$ doped 0.82BNT–0.18BKT (BNKT-xMN) ceramics were prepared by conventional solid-state sintering. The effects of the MN content on the structural and electrical properties of the BNKT-$x$MN ceramics were investigated. The grain size decreases sharply after doping MN. With the increase of the MN content, the phase structure changes from the rhombohedral and tetragonal phase to the tetragonal phase, then to the pseudo-cubic phase. The ferroelectric phase transforms to the relaxor phase. At critical phase (x = 0.03), the maximum positive bipolar strain and unipolar strain are 0.38 and 0.386%, respectively. The corresponding $d^*$$_{33}$ and $d_{33}$ are 767 pm V$^{–1}$ and 158 pC N$^{–1}$, respectively. Meanwhile, the dielectric constant gradually decreases with the increase of the MN content, which flattens the permittivity curves. The large piezoelectric responses are closely associated with the reversible relaxor ferroelectric phase transformation.

In this study, Ho$^{3+}$ doped 0.825K$_{0.5}$Na$_{0.5}$NbO$_3$-0.175Sr(Yb$_{0.5}$Nb$_{0.5}$)O$_3$ luminescence transparent ceramics were prepared via the traditional solid-state sintering method. The structure and optical properties of the ceramics before and after polarization were studied at 40 kV cm$^{-1}$ for 0.5 h. With the increase of Ho content, the phase structure of the ceramics changed from a pseudo-cubic phase to the tripartite and the orthorhombic phases, and the light transmittance decreased. The ceramics demonstrated an up-conversion luminescence characteristic under the excitation of a 980 nm laser, and the emission wavelengths were 550 and 670 nm. The best up-conversion luminescence performance was obtained when the Ho content was 0.1%. Moreover, the polarization markedly enhanced the luminescence performance of the 0.825K$_{0.5}$Na$_{0.5}$NbO$_3$-0.175Sr(Yb$_{0.5}$Nb$_{0.5}$)O$_3$-0.1%Ho ceramics due to the increased possibility of energy-level radiative transition of rare-earth Ho$^{3+}$ ions and reduction of the $E$$_g$ value of the ceramic.

The traditional solid-phase reaction method was used to dope the 0.94(k$_{0.5}$Na$_{0.5}$)NbO$_3$–0.06Sr(Zn$_{1/3}$Nb$_{2/3}$)O$_3$ (0.94KNN–0.06SZN) with rare-earth Er$^{3+}$, showing that the transparent ferroelectric ceramics have both up-conversion luminescence. Also the changes in the phase structure, optoelectronic properties of the ceramics after Er$^{3+}$ doping were investigated. The results show that the doping of Er$^{3+}$ has no significant effect on the phase structure, dielectric constant, coercivity field and residual polarization intensity of the ceramics. With the increase of Er$^{3+}$ content, the saturation polarization intensity shows a trend of decreasing and then increasing, and the dielectric constant first decreases and then stabilizes. The large amount of Er$^{3+}$ also greatly reduced the light transmission of the ceramics. In addition, the doping of Er$^{3+}$ gives the ceramics new properties. Under 980 nm laser excitation, the ceramics exhibit luminescent emission bands at 533, 554 nm (green) and 672 nm (red). The luminous intensity of the ceramic first strengthens with the increase of Er$^{3+}$ content and then weakens, and the strongest luminous intensity is obtained when the Er$^{3+}$ content is 1.00% mol. Transparent ferroelectric ceramics with light-emitting functions will have a broad application prospect in the field of photoelectric crossover.

To protect crops and improve yield, pesticides have been widely used in agricultural production. In this case, the detection of toxic residues in agricultural products is of great significance. To achieve that, spectroscopy is a commonly used analytical method, which combines the characteristics of low detection limit, wide linear range and high accuracy. At the same time, they provide simple, low-cost, fast and on-site results. The pesticide residue detection instruments based on spectral analysis have shown advantages and broad application prospects in the instrument market. In this paper, detection methods of pesticide residues based on fluorescence spectrometry, UV–vis (ultraviolet visible) spectrometry, as well as SERS (surface-enhanced Raman scattering) spectrometry are reviewed. This paper analyses and summarizes the research progress of different types of spectrometry in the detection of pesticide residues, and points outthat with the development of detection and monitoring technology, the corresponding rapid detection instrument for pesticide residues has become an indispensable tool in society.