911 research outputs found
СУЧАСНІ ПІДХОДИ ДО ПОНЯТТЯ ТА КЛАСИФІКАЦІЇ РЕСУРСІВ І РЕСУРСНОГО ЗАБЕЗПЕЧЕННЯ
Get PDFThe article analyzes modern approaches to the definition and classification of the term "resource", "resource support". Suggested a specific classification of resources, proceeding from the properties of resources that will allow choosing the optimal (effective) level of resource use. The analysis revealed new approaches to resource supply, that conventional called static and managerial-logistic, which can be used to ensure the defense capability of the state. It is confirmed that resource support is a complex and multidimensional process. It is proved that in the context of provision of mobilization training, the managerial-logistic approach is more acceptable. The features of the resource support of the mobilization preparation of the state are determined
Paracryptotropa Tkach, Chermak & Patitucci 2023, gen. nov.
No full text<i>Paracryptotropa</i> Tkach, Chermak & Patitucci gen. nov. <p> <i>Diagnosis:</i> Very small digeneans. Body broad, flaưened, with rounded anterior and posterior ends. Tegument armed with minute spines densely covering entire body. Oral sucker subterminal; ventral sucker in middle third of body. Prepharynx very short; pharynx rounded; oesophagus short. Caecal bifurcation immediately anterior to ventral sucker; caeca short, terminating approximately at level of middle of ovary. Testes in posterior half of body, very large, distinctly lobed, opposite, longitudinally elongated, post-ovarian. Copulatory pouch dorsal to ventral sucker; proximal and distal ends of copulatory pouch extend beyond ventral sucker; anterior end of copulatory pouch comma-shaped, curved towards dorsal surface of body. Genital pore submedian, sinistral, immediately extracaecal, at level of caecal bifurcation. Ovary entire, immediately posterodextral to ventral sucker, pretesticular. Vitellarium extensive, in the form of numerous irregularly shaped follicles forming fields of follicles from the level of pharynx to posterior end of body. There are almost no follicles in testicular area, although there are narrow fields of follicles immediately posterior to testes. Some vitelline follicles are positioned in middle third of body between testes. Uterus filling the space between ventral sucker and testes, extending posteriorly between testes to level of mid-length of testes. Metraterm weakly defined. Uterus with numerous eggs. Excretory pore terminal, excretory vesicle Y-shaped.</p> <p> <i>ZooBank registration:</i> urn:lsid:zoobank.org:act: 23E89889- AF9A-452F-9F3D-A29E5FA50755.</p>Published as part of <i>Tkach, Vasyl V., Chermak, Taylor P., Patitucci, Kaylyn K., Greiman, Stephen E., Binh, Tran Thi & Olson, Peter D., 2023, Jumping continents and major host lineages: phylogeny and diversity of the enigmatic Cryptotropidae (Platyhelminthes: Digenea), pp. 533-552 in Zoological Journal of the Linnean Society 199 (2)</i> on pages 547-549, DOI: 10.1093/zoolinnean/zlad037, <a href="http://zenodo.org/record/8426187">http://zenodo.org/record/8426187</a>
Armadoatrium Tkach, Chermak & Olson 2023, gen.nov.
No full text<p> <i>Armadoatrium</i> Tkach, Chermak & Olson <b>gen.nov.</b></p> <p> <i>Diagnosis:</i> Body linguiform, slender. Tegument almost entirely covered with small spines, which diminish somewhat in size towards the posterior end of the body. Oral sucker well developed, subterminal. Prepharynx absent. Pharynx well developed. Oesophagus long. Intestinal bifurcation in posterior forebody. Caeca extend posteriorly well past ventral sucker, but do not reach testes. Genital atrium dorso-sinistral, extracaecal, in ventral sucker region. Genital atrium aperture surrounded by digitiform spines.</p> <p>Two testes, nearly opposite, slightly diagonal, in posterior third of body. Copulatory pouch large, comma-shaped, containing winding seminal vesicle, ejaculatory canal and prostatic glands. Everted cirrus not observed. Proximal end of copulatory pouch extends posteriorly far beyond ventral sucker. Fibrous male accessory pouch (stylet pouch), containing protractible stylet-like rod, situated postero-sinistrally to ventral sucker, its proximal end immediately posterior to ventral sucker.</p> <p>Ovary subspherical, situated dextrally to proximal end of copulatory pouch, between copulatory pouch and seminal receptacle. Seminal receptacle voluminous, immediately posterior to ovary. Vitellarium consisting of numerous small follicles of unequal size and shape, distributed peripherally around central region of body occupied by gonads, uterus and terminal genitalia. Vitelline follicles reach posterior end of body and mid-distance between suckers anteriorly. Mehlis’ gland situated between less testes and proximal end of copulatory pouch. Laurer’s canal not observed. Uterus ventral to gonads, extending posteriorly between testes, occupying space between gonads and expanding posteriorly between testes and laterally beyond testes. Metraterm with weak musculature. Uterine loops not very numerous, mainly in hindbody, passing between testes and almost reaching posterior end of body. Uterus containing numerous operculate eggs. Excretory pore terminal. Excretory vesicle not fully observed, its stem reaching at least mid-level of testes; remainder of excretory vesicle is obscured by uterus.</p> <p>In intestine of bats, Philippines.</p> <p> <i>Type species:</i> <i>Armadoatrium bushae</i> (Chermak & Tkach 2022) comb. nov.</p> <p> <i>ZooBank registration:</i> urn:lsid:zoobank.org:act: D716D46B-5801-45E0-B52B-48173299FA2B.</p>Published as part of <i>Tkach, Vasyl V., Chermak, Taylor P., Patitucci, Kaylyn K., Greiman, Stephen E., Binh, Tran Thi & Olson, Peter D., 2023, Jumping continents and major host lineages: phylogeny and diversity of the enigmatic Cryptotropidae (Platyhelminthes: Digenea), pp. 533-552 in Zoological Journal of the Linnean Society 199 (2)</i> on page 538, DOI: 10.1093/zoolinnean/zlad037, <a href="http://zenodo.org/record/8426187">http://zenodo.org/record/8426187</a>
Neoastiotrema trituri Tkach 2008
No full textNeoastiotrema trituri (Grabda, 1959) Tkach, 2008 (Fig. 17) (Syn. Astiotrema trituri Grabda, 1959) Records. 1. Grabda (1959a, 1959b); 2. Sharpilo & Iskova (1989); 3. Tkach (2008). Remarks. Grabda (1959a) described A. trituri from the small intestine of the smooth, northern smooth or common newt, Lissotriton vulgaris (Linnaeus) (syn. Triturus vulgaris Dunn) (Caudata: Salamandridae), from Lake Mamry in northeastern Poland. Astiotrema trituri was distinguished from all Astiotrema species by (i) the position of the posterior testis near the posterior extremity of the body and posterior to the ends of the ceca, (ii) the much smaller cirrus pouch, and (iii) very large eggs – “almost double-sized” (48–61; 54 × 25–31; 29). That same year, Grabda (1959b) elucidated that A. trituri has life-cycle patterns identical to that of members of the Plagiorchioidea and concluded that the first intermediate host was a pulmonate snail, the great ramshorn, Planorbarius corneus (Linnaeus) (syn. Coretus corneus [Linnaeus]) (Gastropoda: Planorbidae). The second intermediate hosts included some cladoceran species: Simocephalus exspinosus (De Geer), Ceriodaphnia reticulata (Jurine), Daphnia magna Straus (Anomopoda: Daphniidae) and Eurycercus lamellatus (Müller) (Anomopoda: Eurycercidae). The development of this parasite includes the formation of a sporocyst and a xiphidiocercaria. Molecular characterization by Tkach (2008) of some taxa of Astiotrema including A. reniferum , A. monticellii (= P. monticellii), A. turneri (= H. turneri) and A. trituri demonstrated that the first three taxa formed a monophyletic clade closest to the heterophyids in contrast to A. trituri which clustered very close to Plagiorchis Lühe, 1899. Concerning A. trituri , it possesses a typical plagiorchiid-like bipartite seminal vesicle, whereas the other three species of Astiotrema (sensu lato) in the analysis of Tkach (2008) possess an undivided, sac-like seminal vesicle. Based on life-cycle patterns of A. monticellii (= P. monticellii) examined by Shevchenko & Vergun (1960), Tkach (2008) referred that: (i) the first intermediate host of A. monticellii (= P. monticellii) is the prosobranch (gilled) snail Bithynia leachii (Sheppard) (Gastropoda: Bithyniidae), not a pulmonate one as described for A. trituri; (ii) amphibians serve as the definitive host for A. trituri (see Grabda 1959b) whereas amphibians represent intermediate hosts for A. monticellii (= P. monticellii) (Shevchenko & Vergun 1960); and (iii) the development of A. monticellii (= P. monticellii) includes the formation of cercariae from the Pleurolophocerca group within rediae (see Shevchenko & Vergun 1960), which is typical for members of the Opisthorchioidea. As previous molecular phylogenetic analyses generally indicated that Astiotrema formed a monophyletic clade distinctly separate from all members of the Plagiorchioidea and that clade was, moreover, closer to the Opisthorchioidea (Tkach et al. 2001; Olson et al. 2003), Tkach (2008) removed A. trituri from Astiotrema and transferred it into the Plagiorchiidae. Despite the high similarity between A. trituri and members of Plagiorchis, the position of the right posterior testis (near the posterior extremity and past the cecal ends) vs the left anterior testis (intercecal and separated from right posterior testis by numerous uterine coils) gave justification for separating A. trituri into its own genus, Neoastiotrema, with its type- and only species, N. trituri (see Tkach 2008). Besprozvannykh et al. (2015) demonstrated that Shevchenko & Vergun (1960) most likely described a larva belonging to a member of the Opisthorchioidea and neither the cercaria nor the metacercaria of a species of Astiotrema. In addition, they clarified that the first intermediate host of A. odhneri is a pulmonate snail and not a prosobranch (gilled) one; whereas, the second intermediate host can include pulmonate snails, frog tadpoles, and small fish within which sporocysts and xiphidiocercariae develop, but neither rediae nor pleurolophocercariae form. Besprozvannykh et al. (2015, fig. 2) also demonstrated through 28S rRNA gene sequence data that Astiotrema species clustered away from the Plagiorchioidea and formed a monophyletic clade closer and in a basal position to the Opisthorchioidea. Thus, observations of life-cycle patterns by Besprozvannykh et al. (2015) point out a convergence between both Neoastiotrema and Astiotrema, whereas their phylogenetic results indicate a distant relationship between them. Accordingly, we conclude that: (1) reliance on life cycle patterns for differentiating between these two genera may not be useful; (2) without distinct morphological evidence, morphological data become more confusing and unconvincing for differentiating among morphologically similar taxa; hence, using molecular phylogenetic results and support may illustrate the degree of divergence or convergence and give an indicator for delimitations of species and/or higher ranks; (3) the bipartite vs unipartite nature of the seminal vesicle herein represents a stronger feature for differentiating between these two genera and it can be highly effective in differentiating at higher levels of taxonomy such as families or even superfamilies as stated by Pojmańska et al. (2008) and Tkach (2008).Published as part of Karar, Yasser F. M., Blend, Charles K., Dronen, Norman O. & Adel, Asmaa, 2023, Towards resolving the problematic status of the digenean genus Astiotrema Looss 1900: Taxa excluded from Astiotrema (sensu stricto) with special reference to plagiorchioid genera closely related to the restricted concept of Astiotrema, pp. 445-495 in Zootaxa 5284 (3) on pages 463-464, DOI: 10.11646/zootaxa.5284.3.2, http://zenodo.org/record/792950
Climate Arctic Governance: Perspectives on sub-national data-driven policymaking
No full textPresentation of the member of the University of Lapland team working in the WP7 - Pavel Tkach at Climate Arctic Governance conference in Copenhagen that took place on September 16, 2022, about aspects of Arctic regional climate governance information and knowledge about which the author took from his work in the Arctic PASSION project and subsequent communication with the policymakers
MODERN APPROACHES TO THE CONCEPT AND CLASSIFICATION OF RESOURCES AND RESOURCE SUPPORT
Get PDFThe article analyzes modern approaches to the definition and classification of the term "resource", "resource support". Suggested a specific classification of resources, proceeding from the properties of resources that will allow choosing the optimal (effective) level of resource use. The analysis revealed new approaches to resource supply, that conventional called static and managerial-logistic, which can be used to ensure the defense capability of the state. It is confirmed that resource support is a complex and multidimensional process. It is proved that in the context of provision of mobilization training, the managerial-logistic approach is more acceptable. The features of the resource support of the mobilization preparation of the state are determined
Essays on multidimensional poverty measurement and the dependence among well-being dimensions
Get PDFEvaluating the welfare of nations is high on the research agenda of the economists, practitioners and policy-makers. The literature contributions of the last decades triggered a multivariate perception of the well-being, which is suggested to go beyond the GDP, and created a need for more complex approaches to evaluate the welfare as well as poverty. The first essay investigates the approaches to multivariate poverty measurement and focuses on the composite index approach and the steps involved in it. An important aspect of the multivariate perspective in well-being is the dependence among the underlying indicators. There is a growing evidence in the literature that well-being dimensions are interrelated. This dependence among attributes matters for multidimensional poverty measurement, since income is no longer the only indicator to be considered. However, the reviewed approaches to multivariate poverty measurement do not commonly capture this interdependence. The second essay suggests a copula function as a flexible tool to estimate the dependence among welfare variables. Moreover, it proposes to incorporate the evaluated dependence in the composite indicator. The trade-off among attributes, which is established via the weighting of dimensions, is identified as a possible channel to include the interdependence in the composite indicator. The third essay of this dissertation defines bivariate and multivariate copula-based measures of dependence and applies them using the recent data from the EU-SILC. The results suggest that key dimensions of well-being, i.e. income, education and health, are positively interdependent. In addition, the strength of pairwise and multivariate dependence reinforced in the post-crises period in some European countries. Finally, the last essay proposes a new class of the copula-based multidimensional poverty indices by innovating over the weighting approach. The weighting scheme proposed in this dissertation incorporates the estimated copula-based dependence and contains necessary normative controls to be chosen by the practitioner. The findings of the last essay suggest that the overall poverty is driven not only by the individual shortfalls, but also I by the degree of interdependence among well-being indicators. Considering the proposed copula-based weighting scheme and the proposal of the new class of copula-based poverty indices, this dissertation contributes to the multivariate poverty measurement by suggesting the channel to enclose the dependence structure in the composite indicators. The proposed copula-based methodology will advance the multidimensional poverty analysis and the poverty-reducing policy, which can be designed to address the problem of interdependence of individual achievements
Mykhailo Tkach`s love songs
No full textСтаття присвячена аналізові текстів пісень М. Ткача на тему кохання. Детально розглядаються їхні мотиви, символічно-образна система та художні особливості. На цій основі простежується тісний зв’язок між індивідуальним авторським началом, поетикою народної пісні та традиціями української класичної поезії.Статья посвящена анализу текстов песен М. Ткача на тему любви. Подробно рассматриваются их мотивы, символично-образная система и художественные особенности. На этой основе прослеживается тесная связь между индивидуальным авторским началом, поэтикой народной песни и традициями украинской классической поэзии.This article analyzes Mykhailo Tkach`s love songs. Their motives, symbolic-imaginative system and artistic features are considered here. It was observed that there is a close connection between the author`s style, the poetics of folk song and the traditions of Ukrainian classical poetry
Cerâmicos à base de SrTio3 para aplicações em dispositivos sintonizáveis
Get PDFDoutoramento em Engenharia e Ciências de MateriaisO titanato de estrôncio (ST) é conhecido como um paraeléctrico quantumno qual a permitividade dieléctrica aumenta gradualmente após arrefecimento até cerca de 0 K e nenhuma anomalia do tipo ferroeléctrica é observada. Adependência acentuada da permitividade dieléctrica do campo eléctrico dctorna ST um material atractivo para aplicações em componentes electrónicos sintonizáveis, particularmente em dispositivos para operação à frequência dasmicroondas, que incluem, por exemplo, filtros e modificadores de fase paraantenas. Devido ao valor elevado de permitividade dieléctrica estesdispositivos podem ser miniaturizados e tornados economicamente viáveis.Contudo ST apresenta uma limitação em termos de aplicações para indústriaelectrónica de microondas, na medida em que a capacidade de sintonização(tunability) (definida como a variação da permitividade induzida por um campo dc) adequada é apenas atingida abaixo de ~80 K. A gama de temperaturas desintonização elevada pode ser mudada para temperaturas mais altas atravésde substituições atómicas no local Sr da rede, por exemplo, por Ba. É conhecido que para esta substituição uma fase ferroeléctrica é induzida nassoluções sólidas de BaxSr1-xTiO3(BST) numa gama de temperaturas entre temperaturas 0-400 K. Contudo, perdas (insertion loss) e instabilidade térmicaelevadas para BST, que aumentam com o aumento da concentração de Ba, impõe sérias restrições à sua aplicação nas antenas. Desta forma sãonecessários sistemas alternativas à base de ST, nos quais uma anomalia daresposta dieléctrica seja induzida.
Neste trabalho foi efectuada uma investigação sistemática do efeito de substituições atómicas de Sr e Ti por Mg e Mn na estrutura, microestrutura ecomportamento dieléctrico e ferroeléctrico de cerâmicos de ST. Aspropriedades dieléctricas foram estudadas numa gama alargada detemperaturas, frequências e campos eléctricos.
Os cerâmicos de ST e com substituições a nível dos locais A e B daestrutura de perovesquite por Mg e Mn foram preparados pelo métodoconvencional de mistura de óxidos. A estrutura cristalográfica e microestruturados cerâmicos foi analisada por difracção de RX, espectroscopia de Raman, microscopia electrónica de varrimento (SEM) e de transmissão (TEM) eespectroscopias de energias dispersivas (EDS). Investigação detalhada dadinâmica de rede e o comportamento dieléctrico numa gama alargada de frequências for também efectuada.
A caracterização dieléctrica dos cerâmicos de Sr1-xMgxTiO3, SrTi1-yMgyO3-δ, Sr1-xMnxTiO3 e SrTi1-yMnyO3foi realizada em função da temperatura e frequência, incluindo a caracterização às frequências rádio (rf), microondas (MW), “time-domain terahertz” (TDT), e infravermelho (IR). A dependência dapermitividade dieléctrica do campo eléctrico às frequências rádio foi exploradapara uma possível aplicação como componente sintonizável. A comparaçãodos efeitos de dopantes observados é discutida com base no tamanho, local de ocupação catiónica, carga e estequiometria dos sistemas.
A solubilidade sólida de Mg em ST é restrita a x ≤ 1 % para o caso da substituição nos locais A (Sr1-xMgxTiO3) e restrita a y ≤ 10 % para a ocupação nos locais B (SrTi1-yMgyO3-δ). Verificou-se que o parâmetro de rede aumenta com o aumento da concentração de Mg para SrTi1-yMgyO3-δ e é praticamente invariante para Sr1-xMgxTiO3. A dependência da ocupação do local da rede foi também verificada no crescimento de grão dos cerâmicos. Para SrTi1-yMgyO3-δo tamanho de grão decresce acentuadamente com o aumento daconcentração de Mg. Para Sr1-xMgxTiO3é observada a dependência inversa. Os espectros de micro-Raman e da variação da permitividade dieléctrica coma frequência, numa gama alargada de frequências e as características desintonização dos cerâmicos de Sr1-xMgxTiO3não variam consideravelmente em relação aos cerâmicos de ST não dopados, confirmando a pequena inserçãodo Mg na rede perovesquítica de ST. Os resultados indicam que Mg não induz comportamento ferroeléctrico ou ferroeléctrico relaxor no titanato de estrôncio.Mais ainda, o ajustamento do comportamento dieléctrico observado à lei deBarrett demonstrou que a dopagem com Mg nos locais B da rede “afasta” o sistema da instabilidade ferroeléctrica. Os resultados mostraram para estesistema um endurecimento considerável do modo mole de vibração da redeobservado nos espectros de IR. A permitividade e perda dieléctrica decrescemna região das frequências rádio e também para frequências mais elevadas (THz), acompanhados de um decréscimo da sintonização, de acordo com oendurecimento do modo ferroeléctrico mole. Estes resultados confirmam umaocupação mais favorável do Mg nos locais Ti da rede de ST e mostram a possibilidade de utilizar SrTi1-yMnyO3como guias de onda e ressonador às frequências das microondas.
Para ambas as formulações Sr1-xMnxTiO3 e SrTi1-yMnyO3 o parâmetro de rede, calculado dos perfis de difracção de raios X decresceu com o aumentoda concentração de Mn, mas com diferentes taxas de decréscimo. As análisesde TEM indicaram que a solubilidade de sólida de Mn em Sr1-xMnxTiO3é limitada a x< 3 %, enquanto que as análises de SEM mostraram umdecréscimo acentuado do tamanho de grão dos cerâmicos de SrTi1-yMnyO3. A temperatura da transição de fase estrutural aumentou consideravelmente(acima de 150 K) com a dopagem com Mn nos locais A da rede daperovesquite, enquanto que foi observada a diminuição desta transição paraas amostras dopadas com Mn nos locais B.
A dopagem com Mn nos locais B reduz o valor da permitividade dieléctrica,variação esta que é também acompanhada pelo endurecimento do modo molee diminuição da contribuição do modo mole para a resposta dieléctrica e afastao sistema da instabilidade ferroeléctrica. Mai ainda foi observado umdecréscimo da sintonização dieléctrica, seguida de uma redução dapermitividade dieléctrica dos cerâmicos de SrTi1-yMnyO3.
Em oposição foi observado comportamento polar nos sistema Sr1-xMnxTiO3. As medidas dieléctricas às frequências rádio mostraram um máximo depermitividade difuso a 25-80K, que se desloca para temperaturas mais elevadas com o aumento da frequência de medida e aumento da concentraçãode Mn. A anomalia dieléctrica é também observada na região das microondas e terahertz. A observação do comportamento histerético nas curvas de Pversus E confirma a existência de um estado polar a baixas temperaturas. Aresposta histerética degenera lentamente num comportamento não linearidadeà medida que a temperatura aumenta. O comportamento relaxor observado foiatribuído à formação de dipolos eléctricos e correspondentes camposaleatórios devido às posições não centrais (off-centre position) dos iões Mnnos locais de Sr e à rede polarizável de SrTiO3. A difusividade do máximo implica uma elevada estabilidade térmica do comportamento dieléctrico deSr1-xMnxTiO3, fazendo com que ST dopado com Mn seja um possível candidatopara aplicações como componente electrónico sintonizável. Ainda a gama detemperaturas na qual a constante dieléctrica é sintonizável foi alargada (~70%)e foi obtido o factor de qualidade sintonizável de cerca ~6000, às temperaturasde 75-100 K.Strontium titanate (ST) is known as a quantum paraelectric in which thedielectric permittivity monotonously increases upon cooling down to near 0 Kand no ferroelectric-type anomaly is observed. A strong dc-electric-field dependence of the dielectric permittivity makes ST an attractive material forapplications in tunable electronic components, particularly in several microwavedevices including filters and phase shifting elements in phased array antennas. Due to the high dielectric permittivity, these devices may be miniaturizedand cost-effective. However, ST has limited application in the microwave electronicindustry, since adequate tunability (change in the permittivity induced by a dc field) is achieved only below ~80 K. The temperature range of high tunabilitycan be shifted towards high temperature by means of Sr-site substitution by Ba, for example. Such shift corresponds to an induced ferroelectric phase transitionin BaxSr1-xTiO3 (BST) solid solutions at temperatures in the range of 0-400 K. However, higher insertion loss and thermal instability of barium strontiumtitanate, continuously increasing with Ba concentration, impose seriousrestrictions to its application in phased array antennas. Hence, alternative ST-based systems, in which an anomaly of the dielectric response would beinduced, are required.
In this work, systematic research of Sr- and Ti-site substitutions by Mg andMn on structure, microstructure, dielectric and ferroelectric behaviour of ST ceramics is investigated. The dielectric properties are studied in widetemperature, frequency and electric field ranges.
ST ceramics with Sr- and Ti-site substitutions by Mg and Mn are synthesised by conventional mixed oxide method. The crystallographic and micro structures of the doped ceramics are analysed by X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (SEMand TEM) together with energy dispersive spectroscopy (EDS) techniques. Detailed investigation of the lattice dynamics and dielectric behaviour in a widefrequency range is undertaken also. The dielectric characterisation ofSr1-xMgxTiO3, SrTi1-yMgyO3-δ, Sr1-xMnxTiO3 and SrTi1-yMnyO3 ceramics is performed as a function of temperature and frequency by the radio-frequency (rf), microwave (MW), time-domain terahertz (TDT), and infrared(IR) spectroscopy. The dc-electric-field dependence of permittivity in rf range was explored for possible application as tunable components. A comparison of the observed doping effects is discussed based on ion size, cation site occupancy,charge and chemical stoichiometry in the systems.
It was observed that, the solid solubility of Mg is restricted to x ≤ 1 % for Sr-site occupancy (Sr1-xMgxTiO3) and to y ≤ 10 % for Ti-site occupancy (SrTi1-yMgyO3-δ). The lattice parameter is found to increase with Mg content forSrTi1-yMgyO3-δ system, while it is almost invariant in Sr1-xMgxTiO3one. The dependence on the lattice site occupancy is also verified for the grain growth ofceramics. For SrTi1-yMgyO3-δthe average grain size markedly decreases with increasing Mg content. For Sr1-xMgxTiO3the inverse dependence is observed. The micro-Raman spectra and the wide frequency dielectric properties of Sr1-xMgxTiO3including rf tunability do not differ considerably from the propertiesof undoped SrTiO3, confirming only slight incorporation of Mg into the Sr site ofST perovskite lattice. Mg does not induce ferroelectricity or relaxor-like behaviour in strontium titanate, either located in A- or B-site of the SrTiO3lattice. Moreover, fitting the dielectric behaviour to Barrett’s law demonstratesthat B-site doping drives the system away from the ferroelectric instability. Ti-site Mg doping results in significant stiffening of the soft lattice mode observedin IR reflectivity spectra. Dielectric permittivity and dielectric loss decreases inthe frequency range from radio to THz frequencies accompanied by the decrease of the tunability, in accordance with the stiffened ferroelectric softmode. These results confirm more favourable occupation of Mg at the Ti site ofthe ST lattice and show the possibility of using Ti-site Mg-doped ST as an material for low-loss microwave waveguides and resonators.
For both Sr1-xMnxTiO3 and SrTi1-yMnyO3formulations, the lattice parameter, calculated from XRD profiles, was found to decrease with increasing Mncontent, but with different rates. TEM analysis indicated that the solid solubilityof Mn for Sr1-xMnxTiO3 system is limited to x< 3 %, while SEM analysis revealed a marked decrease of the grain size for SrTi1-yMnyO3ceramic samples. The temperature of the structural phase transition was found toincrease considerably (above 150 K) with Mn doping at Sr site, while reduction of this transition was observed for Mn doping at Ti site.
Ti-site Mn doping reduces thedielectric permittivity value, associated with a soft mode stiffening and a lowering of the soft mode phonon contribution to thedielectric response,and drives the system away from ferroelectric instability. Inaddition, a decrease of the dielectric tunability, following a reduction ofdielectric permittivity was observed in SrTi1-yMnyO3 ceramics.
On the contrary, polar behaviour was found in Sr1-xMnxTiO3 ceramic system. Radio-frequency dielectric measurements showed a diffuse maximum at 25-80 K shifting to higher temperatures with increasing measurement frequency andamount of Mn. The dielectric anomaly is observed in the microwave and terahertz ranges also. The observation of hysteretic behaviour in the Pversus E curves shows the existence of a polar state at low temperatures. Thehysteresis response slowly degenerates into just nonlinearity as thetemperature increases. The observed relaxor-type dielectric behaviour isattributed to the formation of electric dipoles and corresponding random fieldsdue to the off-centre position of Mn2+ion at the Sr site of highly polarisable SrTiO3 lattice. The diffusivity of the peak implies a higher thermal stability of thedielectric behaviour of Sr1-xMnxTiO3 compound, making Mn-doped ST system a possible candidate for the tunable electronic component applications. Moreover, the temperature range where the dielectric constant is tunable was enlarged for Sr1-xMnxTiO3 ceramics comparing with undoped SrTiO3. A higher tunability (~70%) and quality factor for tunable components (~6000) around 75-100 K were obtained as well
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