An optimum design of deep‐space downlinks affected by tropospheric attenuation

In the paper, we propose an optimum design of deep‐space downlinks made with 2 hops, at K_a band and above, in which each hop should be designed for providing half of the total noise‐to‐signal power ratio. We have derived this result from maximizing the ratio between the tropospheric attenuation in the 2‐hop downlink and that in the 1‐hop downlink. The design of the 1st hop (free‐space) of the 2‐hop downlink can reduce the spacecraft power, for the same antennas physical size, by increasing the carrier frequency from K_a band (32 GHz) to W band (80 GHz). This choice is not available in 1‐hop downlink design because of the huge Earth tropospheric attenuation expected in the W frequency band. To show a practical design, we have applied the theory to compare 1‐hop downlink design at 32 GHz to 2‐hop downlink design that adopts 32 or 80 GHz in the 1st hop. The calculations refer to spacecrafts located at two astronomical units (300×10⁶ km, about planet Mars) and to NASA and ESA receiving stations located in Goldstone (California), Cebreros (Madrid, Spain), Canberra and New Norcia (Australia). At 0.1% outage probability, in an average year or in the worst month, 1‐hop downlinks show performance critical or close to fail, because of the large tropospheric attenuation (except at Goldstone), while 2‐hop downlinks always work. Copyright © 2009 John Wiley & Sons, Ltd.     

A method to achieve clear‐sky data‐volume download in satellite links affected by tropospheric attenuation

For data downloading from satellites, the traditional approach of considering the complementary probability distribution, P(A_trop) of the total tropospheric attenuation A_trop (dB), at a frequency, polarization, and elevation angle, may be too pessimistic, and it may lead to large overdesign. If the data volume downloaded in a given observation time T_obs (a day, a week, a month, etc.), with a constant probability of symbol error, is more valuable than the instantaneous symbol, or bit rate (as it may be the case in Earth resources observation or in other services that allow long delays in communicating data), another approach can avoid overdesign, namely the various adaptive coding and modulation techniques. We study a particular time integral of A_trop(t): (i) to define the average efficiency of a radio channel faded by the troposphere and (ii) to design a method that can theoretically achieve the same volume of data downloaded in clear‐sky conditions (no troposphere), even if the radio link is faded by the troposphere. The average efficiency and its bounds can be calculated from the complementary probability distribution of A_trop(t). We explicitly apply the theory to radio links faded by rain, by using the experimental rain‐attenuation time series measured with satellite ITALSAT in a 37.8° slant path, at 18.7, 39.6, and 49.5 GHz at Spino d'Adda (Italy), and to those simulated with the synthetic storm technique. Based on the average efficiency, we define the method that can achieve in T_obs, theoretically, the same data volume as in clear sky, directly applicable to quadrature phase‐shift keying, multiple phase‐shift keying, and Shannon capacity theorem. The method requires a fixed increase in power margin, and bandwidth, compared with clear‐sky conditions, and delivers an average symbol rate equal to the maximum symbol rate obtainable when A_trop(t) = 0. The method can also be used in terrestrial links at any frequency. We compare its theoretical performance with the traditional adaptive coding and modulation techniques and show that, even theoretically, these techniques cannot achieve unitary efficiency as, on the contrary, the novel method can do. Copyright © 2015 John Wiley & Sons, Ltd.     

Optoelectronic Properties of Quasi‐Linear,Self‐Assembled Platinum Complexes: Pt–Pt Distance Dependence

Charge‐carrier mobilities of various self‐assembled platinum complexes were measured by time‐resolved microwave conductivity techniques in the temperature range –80 to +100 °C. Eight compounds were investigated in the present study, including the original Magnus' green salt ([Pt(NH₃)₄][PtCl₄]) and derivatives with the general structure [Pt(NH₂R)₄][PtCl₄], where R denotes an alkyl side chain. In one instance, the chlorines were substituted with bromines. For these complexes, which all consist of a linear backbone of platinum atoms with Pt–Pt distances, d, varying from 3.1 to ≥ 3.6 Å, a strong, inverse correlation was found between d and the one‐dimensional charge‐carrier mobility, Σμ_1D. The highest value of Σμ_1D at room temperature was observed for R = (S)‐3,7‐dimethyloctyl (dmoc) with Σμ_1D ≥ 0.06 cm² V^–1 s^–1. Almost all materials exhibited a charge‐carrier mobility that was relatively independent of the temperature over the range studied. One exceptional compound (R = (R)‐2‐ethylhexyl) showed a pronounced negative temperature dependence of the charge‐carrier mobility; upon decreasing the temperature from +100 °C to –80 °C the charge‐carrier mobility increased by a factor of about ten.     

Evaluation of the feasibility of satellite systems design in the 10–100 GHZ frequency range

We have presented a picture of the total attenuation to be considered in satellite communication and broadcasting systems in the 10–100 GHz frequency range. Although the findings and methodology are of general interest, the numerical results apply to the Italian (mid-latitude) sites of Fucino and Gera Lario and to slant paths of elevation angles 33° and 32° respectively. The rain attenuation probability distribution P(A), of exceeding the value A (dB) at a given carrier frequency in an average year, has been estimated by the synthetic storm technique and an associated formula, presently derived, which links A to frequency for fixed probabilities. The extra fading due to water vapour, clouds, oxygen and scintillations is estimated by applying the ITU-R formulae. After studying how the received carrier power P_R changes as a function of frequency for fixed antenna dimensions and transmitted carrier power P_T, we have carried out an exercise to show what first order values of P_T we need in an ideal QPSK modulation scheme, with a standard uncoded stream of 64 kbit/s, in a complete earth–satellite–earth connection, with regenerative or transparent transponders, for a given maximum bit error rate tolerated by users. After this analysis we have drawn the following conclusions: (a) the results depend very much on the outage probability and on the site; (b) there are two windows at high outage probabilities, e.g. 1%, the first in the 20–50 GHz frequency range and the second beyond 70 GHz; (c) in the frequency range 50–70 GHz any significant service availability level cannot be achieved because of the very large fading due to oxygen; (d) the transmitted power can show sharp minima which depend significantly on the outage probability and on the site; (e) service availability levels better than 99⋅99% of the year cannot be achieved at frequencies of 30 GHz and above, with ground station antennae of 25 cm or less aperture diameter. © 1998 John Wiley & Sons, Ltd.     

A structured Solar System satellite relay constellation network topology design for Earth‐Mars deep space communications

The deep space exploration missions require high quality of communication performance between the Earth stations and various deep space explorers, such as Mars orbiters and rovers. Due to the difficulties on improving the point‐to‐point physical wireless link capacity, it is necessary to study the relay network communications under the structured idea. In this paper, the structured Solar System satellite relay constellation network is proposed for Earth‐Mars deep space communications, including the mission background, mathematic model, topology design, and performance analysis. The satellite relay constellation could be modelled as a 2‐dimensional structure with multiple concentric circle loops and multiple relate satellites on each loop. With the different optimal objectives as shortest path, minimum hops and minimum nodes required under the constraint threshold distance for each hop, both the Monte Carlo method and modified Shortest Path First algorithms are studied to work out the optimal network topology designs. Simulation results show that, our network topology design could satisfy the requirements on continuous dual‐directional end‐to‐end communications between the Earth and Mars over the whole mission life period and guarantee the performance of end‐to‐end multihop links above the lowest boundary.     

Solution‐Processed Small‐Molecule Bulk Heterojunction Ambipolar Transistors

Solution‐processed small‐molecule bulk heterojunction (BHJ) ambipolar organic thin‐film transistors are fabricated based on a combination of [2‐phenylbenzo[d,d']thieno[3,2‐b;4,5‐b']dithiophene (P‐BTDT) : 2‐(4‐n‐octylphenyl)benzo[d,d ']thieno[3,2‐b;4,5‐b']dithiophene (OP‐BTDT)] and C₆₀. Treating high electrical performance vacuum‐deposited P‐BTDT organic semiconductors with a newly developed solution‐processed organic semiconductor material, OP‐BTDT, in an optimized ratio yields a solution‐processed p‐channel organic semiconductor blend with carrier mobility as high as 0.65 cm² V^?1 s^?1. An optimized blending of P‐BTDT:OP‐BTDT with the n‐channel semiconductor, C₆₀, results in a BHJ ambipolar transistor with balanced carrier mobilities for holes and electrons of 0.03 and 0.02 cm² V^?1 s^?1, respectively. Furthermore, a complementary‐like inverter composed of two ambipolar thin‐film transistors is demonstrated, which achieves a gain of 115.     

Flight 2 version of in-orbit test transponder (IOTT2) for on-board regenerative satellites

This paper presents the design and realization of regenerative satellite on-board bypass test equipment. Furthermore, two particular examples of an in-orbit test transponder (IOTT) are discussed in detail. The IOTT1, developed for the first 30/20 GHz ITALSAT satellite (F1), was launched in January of 1991. IOTT1 has been a useful tool during satellite assembly, integration and pre-launch tests. IOTT1 was successfully used to fully characterize the multibeam ITALSAT satellite in orbit. In general, the IOTT functions to bypass the demodulator, the baseband switchboard and the modulator of the multibeam package of the ITALSAT spacecraft payload, providing the ability to fully characterize the satellite's transponders using well-established IOT test techniques. This paper describes and compares the design, fabrication and test of both ITALSAT in-orbit test RF bypass transponders (IOTT1 and IOTT2) mounted on board the ITALSAT multibeam spacecraft, (F1) and (F2), respectively. The IOTT1 contains the first MMIC circuitry ever launched into space on a communications satellite. The improved IOTT2, fabricated for the second 30/20 GHz ITALSAT satellite (F2), is schedule for launch in early 1996. These fully space-qualified designs incorporate COMSAT Laboratories' designed and fabricated MMIC K_u-band amplifiers, lightweight waveguide K_u-band channel filters and electronic power conditioner (EPC) and combined IOTT telemetry/command (T&C) circuitry.     

Implementing polarization shift keying over satellite – system design and measurement results

Polarization shift keying (PolSK) is a digital modulation technique using the state of polarization of an electromagnetic wave as the signalling quantity. PolSK comes from fibre communications, where the channel offers two orthogonal states of polarization. This article develops on the idea to adapt this technology to satellite communications, where similar channel conditions exist. For this purpose, a digital PolSK modem was implemented on a programmable logic board. A proposal for constellation design as well as thoughts on synchronization of PolSK over satellite is presented. The modem was used to demonstrate a 16‐state Polarization Shift Keying link over a commercial satellite in K_u band. Measurements have been conducted in a back‐to‐back setup on intermediate frequency and on a K_u band transponder simulator to assess the impact of path‐length differences, carrier recovery and non‐linearity. Copyright © 2015 John Wiley & Sons, Ltd.     

Efficient Deep‐Blue Organic Light‐Emitting Diodes: Arylamine‐Substituted Oligofluorenes

Novel deep‐blue‐light‐emitting diphenylamino and triphenylamino end‐capped oligofluorenes were synthesized by double palladium‐catalyzed Suzuki cross‐coupling of dibromo‐oligofluorene with the corresponding boronic acid as a key step. These oligofluorenes exhibit deep‐blue emission (λ^em_max = 429–432 nm), low and reversible electrochemical oxidation (highest occupied molecular orbital = 5.15–5.20 eV), high fluorescence quantum yield (Φ_FL = 0.61–0.93), and good thermal properties (glass‐transition temperature, T_g = 99–195 °C and decomposition temperature, T_dec > 450 °C). Remarkably, saturated deep‐blue organic light‐emitting diodes, made from these oligofluorenes as dopant emitters, have been achieved with excellent performance and maximum efficiencies up to 2.9 cd A^–1 at 2 mA cm^–2 (external quantum efficiency of 4.1 %) and with Commission Internationale de l'Éclairage (x,y) coordinates of (0.152,0.08), which is very close to the National Television System Committee standard blue.     

Space communications with variable elevation angle faded by rain: Radio links to the Sun–Earth first Lagrangian point L1

How rain attenuation affects space links with variable elevation angles is not yet fully researched. The aim of this paper is to investigate this topic by simulating rain attenuation at K_a Band, in slant paths with variable elevation angles, with the Synthetic Storm Technique (SST), in links connected with spacecrafts at the Sun–Earth first Lagrangian point L₁, viewed from Spino d'Adda (Italy), Tampa (Florida), White Sands (New Mexico). The input to the SST is a large database of time series of 1‐min rain rate recorded on site, 10 years in Spino d'Adda, 4 years at Tampa and White Sands. After recalling known results on the elevation angle of the Sun (i.e. L₁), θ_s (°), seen from latitude λ (°), I report what seems to be a new result: the mode of the probability density function of θ_s in a year, in the range 0 ≤ λ ≤ 90° ? ε (Earth axis tilt angle ε = 23.44°), coincides with the peak angle found at the day of the Winter solstice at the site, a result valid also for other planets, once their tilt angle is used. Compared to the complementary probability distribution function (pdf) of rain attenuation calculated for a geostationary (GEO) link (fixed elevation angle), the pdf to L₁ depends on the rain‐rate pdf during the contact time with L₁, according to the local climate. I show that, to obtain a good and easier estimate of the rain attenuation pdf in L₁ links, we can consider a GEO link with elevation angle equal to the mean angle and rain rate pdf, both during the contact time, and that the mode angle gives an upper bound to the rain attenuation pdf in the sites considered. Copyright © 2015 John Wiley & Sons, Ltd.     

Polylactide‐block‐Polypeptide‐block‐Polylactide Copolymer Nanoparticles with Tunable Cleavage and Controlled Drug Release

A versatile nanoparticle system is presented in which drug release is triggered by enzymatic polymer cleavage, resulting in a physicochemical change of the carrier. The polylactide‐block‐peptide‐block‐polylactide triblock copolymer is generated by initiation of the ring‐opening polymerization of L‐lactide with a complex bifunctional peptide having an enzymatic recognition and cleavage site (Pro‐Leu‐Gly‐Leu‐Ala‐Gly). This triblock copolymer is specifically bisected by matrix metalloproteinase‐2 (MMP‐2), an enzyme overexpressed in tumor tissues. Triblock copolymer nanoparticles formed by nonaqueous emulsion polymerization are readily transferred into aqueous media without aggregation, even in the presence of blood serum. Cleavage of the triblock copolymer leads to a significant decrease of the glass transition temperature (T_g) from 39 °C to 31 °C, likely mediating cargo release under physiological conditions. Selective drug targeting is demonstrated by hampered mitosis and increased cell death resulting from drug release via MMP‐2 specific cleavage of triblock copolymer carrier. On the contrary, nanocarriers having a scrambled (non‐recognizable) peptide sequence do not cause enhanced cytotoxicity, demonstrating the enzyme‐specific cleavage and subsequent drug release. The unique physicochemical properties, cleavage‐dependent cargo release, and tunability of carrier bioactivity by simple peptide exchange highlight the potential of this polymer‐nanoparticle concept as platform for custom‐designed carrier systems.     

A New Material for High‐Temperature Lead‐Free Actuators

Unimorph cantilevers are made from 0.5BaTiO₃‐0.5Sm₂O₃ (BTO‐SmO) self‐assembled vertical heteroepitaxial nanocomposite thin films, grown by PLD on (001) SrTiO₃ single crystal substrates. The films remain piezoelectric up to at least 250 °C without losing any actuation. The longitudinal piezoelectric coefficient, d₃₃, is ≈45 to 50 pm V^?1 measured from room temperature to 250 °C. The transverse piezoelectric coefficient, d₃₁, a key parameter of actuator performance, exceeds PZT (Pb_1–xZr_xTiO₃) films at >200 pm V^?1. Since the d₃₁ coefficient was found to be positive, this opens up exciting new applications opportunities. The possible reasons for d₃₁ > 0 are discussed in the light of 3D strain control in the nanocomposites.     

BPSK and QPSK non‐linear satellite communication system performance in the presence of cochannel interference

Taking the uplink and downlink cochannel interference and noise into account, the analytical expressions are derived for determining the bit error probability in detecting a binary phase‐shift‐keying (BPSK) and a quaternary phase‐shift‐keying (QPSK) Gray coded signal, transmitted over a satellite system exhibiting amplitude modulation‐to‐amplitude modulation (AM/AM) conversion effects and amplitude modulation‐to‐phase modulation (AM/PM) conversion effects. On the basis on the derived theoretic formulae, using real‐life system parameters, numerical results are obtained and presented. We point out the explicit comparisons of satellite communication system performance obtained when a satellite transponder amplifier is modelled by a hard‐limiter and those obtained when both AM/AM and AM/PM non‐linearities of the satellite transponder amplifier are taken into consideration. Copyright © 2003 John Wiley & Sons, Ltd.     

Improvement of charge minority‐carrier lifetime in p(boron)‐type Czochralski silicon by rapid thermal annealing

In p‐type Czochralski‐grown (Cz) silicon a light‐induced degradation of the minority‐carrier lifetime is well known in the literature. Reducing the extent of this degradation would significantly improve the stable effective lifetime and thus the related performance of solar cells. In this work, the reduction of the density of the metastable defect underlying the degradation is performed by rapid thermal annealing (RTA). For a proper analysis it is extremely important to avoid contamination by the RTA furnace. Both, SiN_x and SiO₂ were examined as a barrier layer. A 60 nm SiN_x layer was proven to act as the most effective barrier layer, allowing maintenance of a very high lifetime of 700 μs on 1.25 Ω cm p‐type FZ material. A design‐of‐experiments (DOE) study was used to analyze the effect of five process parameters on the stable effective lifetime. Especially, the plateau temperature shows a strong correlation with τ_d, the stable effective lifetime after light‐induced degradation. The effect of plateau temperature on τ_d of Cz‐ and FZ‐Si wafers is examined in the temperature range of 700–1050°C for plateau time 120 s. It was found that the stable effective lifetime of all RTA‐treated Cz‐wafers is increased compared with the initial stable effective lifetime before processing. The highest increase of stable effective lifetime (by a factor of around 2) is obtained at 900°C with a process time of 120 s. This increase in lifetime is reflected in a reduced concentration of the metastable defect. Copyright © 2001 John Wiley & Sons, Ltd.     

SYNC‐NET: distributed time synchronization in clustered sensor networks

Time synchronization is essential for several ad‐hoc network protocols and applications, such as TDMA scheduling and data aggregation. In this paper, we propose a time synchronization framework for clustered, multi‐hop sensor networks. We assume that relative node synchronization is sufficient, that is, consensus on one time value is not required. Our goal is to divide the network into connected synchronization regions (nodes within two‐hops) and perform inter‐regional synchronization in O(LLSync) × N_iter time, where O(LLSync) denotes the complexity of the underlying low‐level synchronization technique (used for single‐hop synchronization), and N_iter denotes the number of iterations where the low‐level synchronization protocol is invoked. Thus, our main objective is rapid convergence. We propose novel fully distributed protocols, SYNC‐IN and SYNC‐NET, for regional and network synchronization, respectively, and prove that N_iter is O(1) for all protocols. Our framework does not require any special node capabilities (e.g., being global positioning systems (GPS)‐enabled), or the presence of reference nodes in the network. Our framework is also independent of the particular clustering, inter‐cluster routing, and low‐level synchronization protocols. We formulate a density model for analyzing inter‐regional synchronization, and evaluate our protocols via extensive simulations. Copyright © 2007 John Wiley & Sons, Ltd.     

High‐Performance Red,Green, and Blue Electroluminescent Devices Based on Blue Emitters with Small Singlet–Triplet Splitting and Ambipolar Transport Property

Two coordination complex emitters as well as host materials Be(PPI)₂ and Zn(PPI)₂ (PPI = 2‐(1‐phenyl‐1H‐phenanthro[9,10‐d]imidazol‐2‐yl)phenol) are designed, synthesized, and characterized. The incorporation of the metal atom leads to a twisted conformation and rigid molecular structure, which improve the thermal stability of Be(PPI)₂ and Zn(PPI)₂ with high T_d and T_g at around 475 and 217 °C, respectively. The introduction of the electron‐donating phenol group results in the emission color shifting to the deep‐blue region and the emission maximum appears at around 429 nm. This molecular design strategy ensures that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) HOMO and LUMO of Be(PPI)₂ and Zn(PPI)₂ localize on the different moieties of the molecules. Therefore, the two complexes have an ambipolar transport property and a small singlet–triplet splitting of 0.35 eV for Be(PPI)₂ and 0.21 eV for Zn(PPI)₂. An undoped deep‐blue fluorescent organic light‐emitting device (OLED) that uses Be(PPI)₂ as emitter exhibits a maximum power efficiency of 2.5 lm W^?1 with the CIE coordinates of (0.15, 0.09), which are very close to the National Television Standards Committee (NTSC) blue standard (CIE: 0.14, 0.08). Green and red phosphorescent OLEDs (PhOLEDs) that use Be(PPI)₂ and Zn(PPI)₂ as host materials show high performance. Highest power efficiencies of 67.5 lm W^?1 for green PhOLEDs and 21.7 lm W^?1 for red PhOLEDs are achieved. In addition, the Be(PPI)₂‐based devices show low‐efficiency roll‐off behavior, which is attributed to the more balanced carrier‐transport property of Be(PPI)₂.     

Effects of Arylene Diimide Thin Film Growth Conditions on n‐Channel OFET Performance

A series of eight perylene diimide (PDI)‐ and naphthalene diimide (NDI)‐based organic semiconductors was used to fabricate organic field‐effect transistors (OFETs) on bare SiO₂ substrates, with the substrate temperature during film deposition (T_d) varied from 70–130 °C. For the N,N′‐n‐octyl materials that form highly ordered films, the mobility (µ) and current on‐off ratio (I_on/I_off) increase slightly from 70 to 90 °C, and remain relatively constant between 90 and 130 °C. I_on/I_off and µ of dibromo‐PDI‐based OFETs decrease with increasing T_d, while films of N,N′‐1H,1H‐perfluorobutyl dicyanoperylenediimide (PDI‐FCN₂) exhibit dramatic I_on/I_off and µ enhancements with increasing T_d. Increased OFET mobility can be correlated with higher levels of molecular ordering and minimization of film morphology surface irregularities. Additionally, the effects of SiO₂ surface modification with trimethylsilyl and octadecyltrichlorosilyl monolayers, as well as with polystyrene, are investigated for N,N′‐n‐octyl dicyanoperylenediimide (PDI‐8CN₂) and PDI‐FCN₂ films deposited at T_d = 130 °C. The SiO₂ surface treatments have modest effects on PDI‐8CN₂ OFET mobilities, but modulate the mobility and morphology of PDI‐FCN₂ films substantially. Most importantly, the surface treatments result in substantially increased V_th and decreased I_off values for the dicyanoperylenediimide films relative to those grown on SiO₂, resulting in V_th > 0.0 V and I_on/I_off ratios as high as 10⁸. Enhancements in current modulation for these high‐mobility, air‐stable, and solution‐processable n‐type semiconductors, should prove useful in noise‐margin enhancement and further improvements in organic electronics.     

Adaptive frequency‐hopping schemes for CR‐based multi‐link satellite networks

In this paper, we study two dynamic frequency hopping (DFH)–based interference mitigation approaches for satellite communications. These techniques exploit the sensing capabilities of a cognitive radio to predict future interference on the upcoming frequency hops. We consider a topology where multiple low Earth orbit satellites transmit packets to a common geostationary equatorial orbit satellite. The FH sequence of each low Earth orbit–geostationary equatorial orbit link is adjusted according to the outcome of out‐of‐band proactive sensing scheme, performed by a cognitive radio module in the geostationary equatorial orbit satellite. On the basis of sensing results, new frequency assignments are made for the upcoming slots, taking into account the transmit powers, achievable rates, and overhead of modifying the FH sequences. In addition, we ensure that all satellite links are assigned channels such that their minimum signal‐to‐interference‐plus‐noise ratio requirements are met, if such an assignment is possible. We formulate two multi‐objective optimization problems: DFH‐Power and DFH‐Rate. Discrete‐time Markov chain analysis is used to predict future channel conditions, where the number of states are inferred using k‐means clustering, and the state transition probabilities are computed using maximum likelihood estimation. Finally, simulation results are presented to evaluate the effects of different system parameters on the performance of the proposed designs.     

Associating and Tuning Sodium and Oxygen Mixed‐Ion Conduction in Niobium‐Based Perovskites

Pure ionic conductors as solid‐state electrolytes are of high interest in electrochemical energy storage and conversion devices. They systematically involve only one ion as the charge carrier. The association of two mobile ionic species, one positively and the other negatively charged, in a specific network should strongly influence the total ion conduction. Nb⁵⁺‐ (4d⁰) and Ti⁴⁺‐based (3d⁰) derived‐perovskite frameworks containing Na⁺ and O^2? as mobile species are investigated as mixed ion conductors by electrochemical impedance spectroscopy. The design of Na⁺ blocking layers via sandwiched pellet sintered by spark plasma sintering at high temperatures leads to quantified transport number of both ionic charge carriers t_Na+ and t_O2?. In the 350–700 °C temperature range, ionic conductivity can be tuned from major Na⁺ contribution (t_Na+ = 88%) for NaNbO₃ to pure O^2? transport in NaNb_0.9Ti_0.1O_2.95 phase. Such a Ti‐substitution is accompanied with a ≈100‐fold increase in the oxygen conductivity, approaching the best values for pure oxygen conductors in this temperature range. Besides the demonstration of tunable mixed ion conduction with quantifiable cationic and anionic contributions in a single solid‐state structure, a strategy is established from structural analysis to develop other architectures with improved mixed ionic conductivity.     

Domain Engineering of Lead‐Free Li‐Modified (K,Na)NbO3 Polycrystals with Highly Enhanced Piezoelectricity

Aging and re‐poling induced enhancement of piezoelectricity are found in (K,Na)NbO₃ (KNN)‐based lead‐free piezoelectric ceramics. For a compositionally optimized Li‐doped composition, its piezoelectric coefficient d₃₃ can be increased up to 324 pC N^?1 even from a considerably high value (190 pC N^?1) by means of a re‐poling treatment after room‐temperature aging. Such a high d₃₃ value is only reachable in KNN ceramics with complicated modifications using Ta and Sb dopants. High‐angle X‐ray diffraction analysis reveals apparent changes in the crystallographic orientations related to a 90° domain switching before and after the aging and re‐poling process. A possible mechanism considering both defect migration and rotation of spontaneous polarization explains the experimental results. The present study provides a general approach towards piezoelectric response enhancement in KNN‐based piezoelectric ceramics.