Apatite Structure Research Articles

Sintered La10−xNdxSi6O27 (x = 0, 0.1, 0.2, 0.3) by spark plasma sintering and its microstructure and electrical conductivity

La10−xNdxSi6O27 (x = 0, 0.1, 0.2, 0.3) was synthesized via planetary grinding, and dense ceramic discs were prepared using SPS technology. The structure, microstructure, density, open porosity, total conductivity and electronic conductivity of the samples were measured and analyzed, respectively. La10−xNdxSi6O27 is characterized by a hexagonal apatite structure. The elements in the sample are distributed in a uniform manner and the content is consistent with the stoichiometry. The total conductivity of La10−xNdxSi6O27 exhibits an increase with the incorporation of Nd3+ content in the doped samples of x = 0.1, 0.2, and 0.3. The total conductivity of La9.7Nd0.3Si6O27 is the highest, reaching 5.39 × 10−3 S cm−1 at 850 °C. The electron mobility of the sample is less than 1%, which is suitable for use as a solid electrolyte.

The location of cationic substitutions in carbonated biomimetic apatites significantly affects crystal nanomechanics

Bone and teeth are comprised of carbonate-substituted apatites with cationic substitutions, like sodium and potassium. Cations substitute for calcium in the apatite lattice but it is unclear whether they substitute for Ca(1) or Ca(2). Additionally, although we know that anionic substitutions affect the mineral mechanics, it is unclear how cationic substitutions affect mineral stiffness. Here, a combined experimental and theoretical approach using in situ fluid-mediated hydrostatic loading with synchrotron Wide Angle X-ray Scattering (WAXS) and Density Functional Theory (DFT) is used to elucidate the role of CO32− and Na+ or K+ co-substitutions on the atomic structure and mechanics of biomimetic apatites. Comparison of WAXS and DFT results showed that preferential substitutions at the Ca(1) and Ca(2) sites depended on cationic type and concentration, with a preference for Ca(1) at higher levels of co-substitution. Substitution levels and location of the cationic substitution both significantly affected the modulus of the minerals. This presents a new paradigm for the development of biomimetic apatites with multi-property tunability by considering composition and atomic organization.

Exploring the molecular biology of zinc-doped hydroxyapatite nanocomposites as fillers for dental materials: a self-defensive approach targeting bacterial DNA

Abstract Infections during or after the denture filling pose a serious threat to recovery later, and antibiotics are scanty for quick healing. The antibacterial potential of Zn has convinced us to fabricate its composites with hydroxyapatite (HA), which has distinct biological properties. The main aim of the study is to evaluate the antibacterial potential of Zn-doped HA and investigate its molecular interaction with bacterial strains to enhance its defensive ability against bacterial attack. This study investigates the synthesis of zinc-doped hydroxyapatite nano-powder (Zn-HA) as coating and filling materials for dental applications. The co-precipitation technique was used in this regard to obtain the purest form of nanoparticles. The as-prepared Zn-HA samples were characterized by FTIR spectroscopy to assess the interaction of functional groups between components, X-ray diffraction (XRD) to determine percentage crystallinity, SEM to explore the surface morphology of composites, and EDX to confirm the incorporation of Zn in the apatite structure. The crystalline size of Zn-HA decreases from 99 nm to 40 nm with an increase in the doping of Zncl2 from 0 to 2.5g. With increasing the concentration of Zn doping, the effectiveness of antibacterial potential was increased. Due to an increased in the concentration of doped Zn, the Zn ions effectively rupture the bacterial membrane and destroy its DNA. Meanwhile, it shows the highest antibacterial activity against Pseudomonas (20.2±0.02), Klebsiella (25.8±0.05), Bacillus (18.3±0.09), S. aureus (24±0.03), and E. coli (19.3±0.09) with Zn/HA5.It showed that by increasing the concentration of Zinc ions in hydroxyapatite, the antibacterial potential increased. This increased concentration of zinc ions in HA enhances its-defensive ability against the attack of various bacterial strains, this makes it a potential material and enhances its efficacy in dental applications like coating, filling material, or dental restoratives, in inhibiting the growth of bacterial colonies and biofilm formation in the oral cavity. In this way, Zn/HA as an efficient dental composite as a restorative material with enhanced antibacterial potential may help to mitigate the risk of dental infections, promote dental as well as oral health, and overall improve the life of dentine.

Innovative reuse of mineral waste for treatment of a contaminated soil by fluorine: synthesis of hydroxyapatite (HAP) and chemical performance assessments.

This research aimed to introduce a novel method for the valorization of mineral waste, focusing on the development of hydroxyapatite (HAP) as an effective and economical adsorbent for immobilizing fluoride ions (F-) in soil. Hydroxyapatites were produced through the reaction between potassium dihydrogen phosphate (KH2PO4) and calcium-abundant limestone soil (CLS). X-ray diffraction analyses revealed that the primary phases in HAPCLS were brushite (CaHPO5·2H2O) and hydroxyapatite (Ca10(PO4)6(OH)2). The FTIR spectra exhibited characteristics akin to natural HAP, including the presence of orthophosphate groups (PO43-), hydroxyl groups (OH-), and both A/B types of carbonates in the apatite structure. The morphology of the synthesized HAP, as observed through SEM-EDS, was consistent with that of phosphocalcic hydroxyapatite crystals. The EDS results indicated a Ca/P atomic ratio of 1.7 for HAPCLS, aligning closely with the typical hydroxyapatite stoichiometry (Ca/P = 1.67). The application of HAP to reduce fluoride (F-) levels in soil proved to be successful; introducing 1% of various HAP formulations reduced the fluoride concentration from 51.4mg/kg in untreated soil to levels below the IWSI limit (10mg/kg), achieving a reduction to 8.1mg/kg for HAPCLS. The sequential extraction of fluoride demonstrated that after soil treatment, fluoride was predominantly removed from the residual fraction (Fraction 4) and was effectively sequestered by the hydroxyapatites (Ca10(PO4)6(OH)2) through anionic exchange with hydroxide ions (OH-), resulting in the formation of stable and insoluble fluorapatite (Ca10(PO4)6F2).

Investigation of the CMAS corrosion resistance of high-entropy oxides through B-site cation doping

High-temperature erosion caused by calcium magnesium aluminum silicate (CMAS) poses a significant challenge to the advancement of thermal barrier coatings (TBCs). In this investigation, four multi-component A2B2O7 type oxide TBC materials, namely Eu2(Y0.2Ce0.2Zr0.2Hf0.2Ta0.2)2O7, Eu2(Y0.2Yb0.2Ce0.2Nb0.2Ta0.2)2O7, Eu2(Y0.2Yb0.2Zr0.2Nb0.2Ta0.2)2O7, and Eu2(Y0.2Yb0.2Hf0.2Nb0.2Ta0.2)2O7, were synthesized using the solid-state method. We investigated the corrosion behavior of molten CMAS on the samples at 1300 °C for durations of 1 h, 20 h, and 50 h. The resulting corrosion products consist of apatite and cubic fluorite structures. Our analysis reveals that as the ionic radius of RE3+ increases, the stability of the apatite structure improves. Furthermore, molten CMAS exhibits varied wetting behaviors on different substrates at the same temperature. A higher contact angle suggests that the CMAS melt will encounter difficulty in diffusing and penetrating the substrate surface. This research will contribute to the development of TBC materials with enhanced resistance to CMAS corrosion.

Synthesis and characteristics of densified GDC-LSO composite as a new apatite-based electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFC)

Developing solid-state ionic conductors with desirable charge-transport efficiency and reasonable durability is a fundamental and long-lasting challenge for solid-oxide fuel cells (SOFCs). Ceria-based electrolytes, as one of the most common types of electrolytes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs), offer a high surface-exchange coefficient and faster kinetics in the triple phase boundaries (TPBs); however, they suffer to some extent of electronic conductivity in the reducing atmosphere and gradual phase transitions. Here in this work, we have reported a novel co-doped IT-SOFC electrolyte composite combining the apatite structure of Lanthanum Silicate (LSO) with the fluorite structure of Gadolinium-doped Ceria (GDC), which showed a high ionic conductivity and a minimal electronic leak. The resulting GDC-LSO composite electrolyte also achieved an OCV (open-circuit voltage) of 1 V at 800 °C, implying a significant improvement in the OCV values reported for the typical ceria-based electrolytes (∼0.75 V). The sample was prepared using 40 wt% GDC and 60 wt% LSO (40GDC-60LSO) showed a maximum electrical conductivity of 25 mS cm−1 at 800 °C with good densification properties (>95 % relative density). The cell electrochemical performance measurement was conducted using a 3.0 vol% humified H2 stream at the anode side while the cathode side was exposed to the air at 800 °C. The interdiffusion of cations between La3+ in the LSO phase and Ce4+ and Gd3+ in the GDC phase was detected by XRD and EDX results after sintering samples at 1500 °C for 4 h using 0.5 wt% PVA or 0.5 wt% Ethyl cellulose (EC) as the binder. The proposed GDC-LSO composite could help better understand the influence of compositional constituents and processing variables on the densification and electrical properties of the electrolyte materials for the IT-SOFCs.

Effect of Rare Earth Ion Substitution on Phase Decomposition of Apatite Structure.

The paper describes an investigation of phase decomposition of apatite lattice doped with rare earth ions (cerium, samarium, and holmium) at temperatures ranging from 25-1200 °C. The rare-earth ion-doped apatite minerals were synthesized using the sol-gel method. In situ high-temperature powder X-ray diffraction (XRD) was used to observe the phase changes and the lattice parameters were analyzed to ascertain the crystallographic transformations. The expansion coefficient of the compounds was determined, and it was found that the c-axis was the most expandable due to relatively weak chemical bonds along the c-crystallographic axis. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to examine the decomposition properties of the materials. Due to rare earth ion doping, the produced materials had slightly variable decomposition behaviour. The cerium and samarium ions were present in multiple oxidation states (Ce3+, Ce4+, Sm3+, Sm2+), whereas only Ho3+ ions were observed. Rare earth ion substitution affects tri-calcium phosphate proportion during decomposition by regulating concentrations of vacancies. X-ray photoelectron spectroscopy (XPS) analysis indicated that cerium and samarium ion-doped apatite yielded only 25 % tricalcium phosphate during decomposition. This finding advances our understanding of apatite structures, with implications for various high-temperature processes like calcination, sintering, hydrothermal processing, and plasma spraying.

Influence of Fe2O3 on synthesis, structure, hardness, and radiation shielding properties of Apatite–Wollastonite (AW) glass ceramics for bone implantation and shielding applications

This paper explores the important impact of Fe2O3 on the synthesis, structure, hardness, and radiation shielding characteristics of Apatite–Wollastonite (AW) glass ceramics for bone implantation and shielding application. The prepared studied samples were prepared and the effects of Fe2O3 addition on the synthesis process, density, and different physical and structural parameters comprehensively investigated. Additionally, the radiation shielding properties were determined by using PHITS simulation code and XCOM calculations for all samples. The results reveal that there is a significant impact of Fe2O3 addition on density, hardness, and radiation shielding of AW glass ceramics. The Vickers hardness values were calculated as 547, 598, and 621 Hv in measurements under 0.1 kg load., the density values are found to be as 2.87, 3.07 and 3.28 g/cm3 for AW, Aw -1Fe, and Aw -2Fe, respectively. The highest linear attenuation coefficient in the AW- 2Fe is 0.096 cm−1, Aw -1Fe showed 0.084 cm−1 and AW gave 0.072 cm−1 at 6 MeV. This study underscores the pivotal role of Fe2O3 as a multifaceted modifier in tailoring the properties of AW glass ceramics for bone implantation and other diverse applications extending from medical imaging to radiation and charged ions shielding.

Exploring the functional abilities of PVA–combeite composites as potential candidates for bone substitutes

Abstract The field of biomaterials continually seeks novel materials to meet the requirements of bone tissue engineering. This manuscript explores polyvinyl alcohol (PVA)–combeite composites. The composites were characterized using X-ray diffraction and scanning electron microscopy. Notably, the X-ray diffraction patterns unveil a combination of amorphous and crystalline regions attributed to PVA and combeite, respectively. More importantly, PVA–combeite composites exhibit reduced swelling and degradation rates compared to pure PVA. The percentage swelling and degradation values (%) for the prepared materials fall within the range of 190–340 and 55–75, respectively. The spherical apatite structures formed post the immersion in Hanks’ Balanced Salt Solution indicate that these materials could be used in the field of bone tissue engineering.

On the role of vanadium in the structure and properties of calcium-bismuth-sodium oxyapatite

This study explores the possibility of obtaining solid solutions with the composition Ca8BiNa(PO4)6-x(VO4)xO (0 < x ≤ 6) and investigating their physicochemical and medicobiological properties. Using solid-state synthesis method, only the composition Ca8BiNa(PO4)5·5(VO4)0·5O was obtained, while for other values of x, mixtures of apatite and secondary phases or mixtures of various vanadates and phosphates without the target apatite structure were obtained. The study considers the dimensional crystal chemical factors influencing the possibility of forming solid solutions in a wide range of compositions. The crystal structure of Ca8BiNa(PO4)5·5(VO4)0·5O was refined by the Rietveld method (a = 9.45154(37) Å, c = 6.93659(28) Å, V = 536.638(47) Å3, R-Bragg = 3.718 %) and confirmed by group analysis of the IR spectrum. Standard MTT test showed that this substance is not cytotoxic at dilutions of 1:2 and higher. No bactericidal activity against S. aureus and E. coli cultures was observed.

A nontoxic strontium nanoparticle that holds the potential to act upon osteocompetent cells: An in vitro and in vivo characterization.

Estrogen deficiency, long-term immobilization, and/or aging are commonly related to bone mass loss, thus increasing the risk of fractures. One option for bone replacement in injuries caused by either traumas or pathologies is the use of orthopedic cement based on polymethylmethacrylate (PMMA). Nevertheless, its reduced bioactivity may induce long-term detachment from the host tissue, resulting in the failure of the implant. In view of this problem, we developed an alternative PMMA-based porous cement (pPMMA) that favors cell invasion and improves osteointegration with better biocompatibility. The cement composition was changed by adding bioactive strontium-nanoparticles that mimic the structure of bone apatite. The nanoparticles were characterized regarding their physical-chemical properties, and their effects on osteoblasts and osteoclast cultures were assessed. Initial in vivo tests were also performed using 16 New Zealand rabbits as animal models, in which the pPMMA-cement containing the strontium nanoparticles were implanted. We showed that the apatite nanoparticles in which 90% of Ca2+ ions were substituted by Sr2+ (NanoSr 90%) upregulated TNAP activity and increased matrix mineralization. Moreover, at the molecular level, NanoSr 90% upregulated the mRNA expression levels of, Sp7, and OCN. Runx2 was increased at both mRNA and protein levels. In parallel, in vivo tests revealed that pPMMA-cement containing NanoSr 90%, upregulated two markers of bone maturation, OCN and BMP2, as well as the formation of apatite minerals after implantation in the femur of rabbits. The overall data support that strontium nanoparticles hold the potential to up-regulate mineralization in osteoblasts when associated with synthetic biomaterials.

Synthesis, some Physicochemical and Biomedical Properties of colored Apatite‐Structured Compounds with Mn5+ and Cr5+

AbstractDevelopment of new non‐toxic pigments of a wide range of applications (from coloring of bone cements to aesthetic cosmetology, including tattooing) of blue and green shades is an urgent task. In the present work, colored compounds with apatite structure were synthesized by solid‐phase method. The obtained products were crystallized in hexagonal syngony of P63/m space group. The alloying elements – chromophores Mn5+ and Cr5+ in tetrahedrally coordinated positions – were responsible for sky‐blue and turquoise colors of the compounds, respectively. The conducted complex study (crystal structure, IR spectroscopy, color measurements, diffuse reflectance spectroscopy, electron paramagnetic resonance, cytotoxicity, surface morphology) of the colored compounds opens new opportunities for the development of alternative pigments of similar color range and expansion of the field of application of pigments based on compounds of apatite structural type. The results of in vitro study of cytotoxicity demonstrated the potential suitability of sky‐blue color compound (Mn‐containing apatite) for further creation of cold pigments on its basis for tattoo ink and bone cement coloring.

Luminescent manifestations of ytterbium ions in the crystal structure of silicate apatite

The manifestation of ytterbium ions in the microcrystals of the Sr2Y6.8YbSi6O26:Er0.2 solid solution with apatite structure was studied on the basis of low-temperature photoluminescence (PL) spectroscopy and spectral-kinetic measurement data. Intracenter down-conversion luminescence of Er3+ ions in the visible and IR ranges was detected. Up-conversion luminescence of Er3+ ions is observed upon IR excitation due to excitation of Yb3+ ions and subsequent energy transfer Yb3+ → Er3+. Overlapping bands at 412 and 430 nm with a Stokes shift of less than 0.3 eV are observed in the PL spectra at room temperature. These emission bands are assigned to the spin-allowed and spin-forbidden 4f135d → 4f14 transitions from the low-spin and high-spin exciting states of Yb2+ ion, respectively. The PL decay kinetics for transitions from the low-spin states is characterized by a dominant component τ = 0.39 ns. An alternative model of Yb3+ luminescence center associated with a charge transfer band does not explain the data of low-temperature (5K) PL spectroscopy. At T = 5 K, a new wide emission band with a maximum at 696 nm and a Stokes shift of 1.1 eV appears in the PL spectrum. Two options of this PL band nature are considered. The first is the luminescence of defects having a vacancy nature. The second possible option is the manifestation of anomalous luminescence of Yb2+ ions, which occupy a different crystallographic position in the apatite crystal structure.

Investigating the mechanism of formation of Ca-rich Ca[sbnd]Yb apatite that forms from the Yb-silicate–CMAS reaction at 1300°C

The formation mechanism and structure of Ca-rich CaYb apatite, which forms from the corrosion of Yb-silicate based coatings with CMAS at 1300°C in air for 48 h was investigated. X-ray photoelectron spectroscopy (XPS) was used to determine the bond type and oxidation states of the apatite. XPS data showed that the Si2p peaks are related to silicates, while the Ca2p and Yb4d are linked to apatite structures. The mechanism of growth for the apatite is proposed using the Wagner-Hauffe oxidation principle and the Kröger-Vink notations. The formation mechanism of the apatite-structure reaction phase is by substitutional diffusion, which is governed by the movement (formation and destruction) of point defects within the Yb2O3 lattice, particularly oxygen vacancies and electron holes. When Ca2+ substitutes Yb3+ in its lattice position, this results in the formation of anionic vacancies, which leads to more Ca2+ diffusion. The diffusion process continues until vacancies can no longer form to achieve electroneutrality, which leads to the newly formed Yb–Ca–Si being saturated with cations. Thus, based on this investigation, it is assumed that a CaYb silicate oxyapatite coatings can suppress the vacancy formation mechanism by containing high Ca and Si content which can thus decrease the ionic diffusion from CMAS melt into the EBC lattice. This can be the premises of a more CMAS-resistant coating family.

Exploring the various effects of Cu doping in hydroxyapatite nanoparticle

Adding foreign ions to hydroxyapatite (HAp) is a popular approach for improving its properties. This study focuses on the effects of calcium substitution with copper in HAp. Instead of calcium, copper ions were doped into the structure of hydroxyapatite nanoparticles at 1%, 3%, and 5% concentrations. XRD analysis showed that the amount of substituted copper was less than needed to generate a distinct phase, yet its lattice parameters and crystallinity slightly decreased. Further, the results of degradation tests revealed that copper doping in hydroxyapatite doubled calcium ion release in water. The incorporation of copper into the apatite structure also boosted the HAp zeta potential and FBS protein adsorption onto powders. According to antibacterial investigations, a concentration of 200 mg/ml of hydroxyapatite containing 5% copper was sufficient to effectively eradicate E. coli and S. aureus bacteria. Furthermore, copper improved hydroxyapatite biocompatibility. Alkaline phosphatase activity and alizarin red tests showed that copper in hydroxyapatite did not inhibit stem cell differentiation into osteoblasts. Also, the scratch test demonstrated that copper-containing hydroxyapatite extract increased HUVEC cell migration. Overall, our findings demonstrated the utility of incorporating copper into the structure of hydroxyapatite from several perspectives, including the induction of antibacterial characteristics, biocompatibility, and angiogenesis.

Design of the electronic structure and properties of calcium apatites via isomorphic modification of the cation sublattice, and prospects of their application

The evolution of the valence band, charge states of atoms, and optical and vibrational spectra in compounds Ca10−xMx(PO4)xY2, M = Fe, Ni, Cu, Mg; Y = OH, Cl, F was studied by using XPS, infrared, and optical spectroscopy, with the addition of quantum mechanics calculations. The changes in the bandgap in these compounds were analyzed. Isomorphic substitution of calcium ions in the cationic sublattice of calcium hydroxyapatite by metal ions changes the shape of the curve that represents the occupied part of the valence band only slightly. It retains a pronounced gapped character with different lengths of individual subbands—the upper and lower parts of the valence band. It is shown that the predominant position of rare earth and uranium atoms in the apatite structure is the Ca(2)-position. Isomorphic substitution of calcium atoms by metal atoms (Fe, Ni, Cu, Mg) in the apatite structure in the range of 1%–2% of atoms leads to the narrowing of the energy gap. The most significant narrowing is observed when calcium is substituted by nickel and copper. The theoretically calculated bandgap width in calcium apatites can be well described in terms of the generalized gradient approximation. The design of the structure of calcium apatites via the method of isomorphic substitutions in the cation sublattice makes it possible to control the bandgap width, thus expanding the field of practical application of these compounds.

On the dynamical stability of copper-doped lead apatite

The recent claim of room temperature superconductivity in a copper-doped lead apatite compound, called LK-99, has sparked remarkable interest and controversy. Subsequent experiments have largely failed to reproduce the claimed superconductivity, while theoretical works have identified multiple key features including strong electronic correlation, structural instabilities, and dopability constraints. A puzzling claim of several recent theoretical studies is that both parent and copper-doped lead apatite structures are dynamically unstable at the harmonic level, questioning decades of experimental reports of the parent compound structures and the recently proposed copper-doped structures. In this work, we demonstrate that both parent and copper-doped lead apatite structures are dynamically stable at room temperature. Anharmonic phonon–phonon interactions play a key role in stabilizing some copper-doped phases, while most phases are largely stable even at the harmonic level. We also show that dynamical stability depends on both volume and correlation strength, suggesting controllable ways of exploring the copper-doped lead apatite structural phase diagram. Our results fully reconcile the theoretical description of the structures of both parent and copper-doped lead apatite with the experiment.

Influence of Magnesium Source on the Mechanochemical Synthesis of Magnesium-Substituted Hydroxyapatite.

Magnesium, as one of the most abundant cations in the human body, plays an important role in both physiological and pathological processes. In this study, it was shown that a promising biomedical material, Mg-substituted hydroxyapatite (Mg-HA), can be synthesized via a fast mechanochemical method. For this method, the nature of magnesium-containing carriers was shown to be important. When using magnesium oxide as a source of magnesium, the partial insertion of magnesium cations into the apatite structure occurs. In contrast, when magnesium hydroxide or monomagnesium phosphate is used, single-phase Mg-HA is formed. Both experimental and theoretical investigations showed that an increase in the Mg content leads to a decrease in the lattice parameters and unit cell volume of Mg-HA. Density functional theory calculations showed the high sensitivity of the lattice parameters to the crystallographic position of the calcium site substituted by magnesium. It was shown experimentally that the insertion of magnesium cations decreases the thermal stability of hydroxyapatite. The thermal decomposition of Mg-HA leads to the formation of a mixture of stoichiometric HA, magnesium oxide, and Mg-substituted tricalcium phosphate phases.

Novel synthesis and crystallographic results of zinc substituted hydroxyapatite with high thermal stability

Hydroxyapatite (CaHap) doped with different amounts of Zn(II) has been studied by complementary techniques, X-ray powder diffraction (XRPD), thermogravimetry (TGA) and infrared spectroscopy (FTIR), the latter including the examination of samples treated at different temperatures. The studied samples have been synthesized at 98 °C by a precipitation method by a reaction of solutions of Ca(OH)2, H3PO4 and ZnCl2. The analysis of FTIR and XRPD data by Rietveld method suggests that at low Zn(II) concentration, the Zn(II) ions exhibits some preference to occupy the Ca2 site of the apatite structure. However, to increasing concentrations up to 6.2 wt % of Zn(II), XRPD and FTIR data as well as those from thermal treated samples indicate that Zn(II) ions would exhibit some preference to occupy the Ca1 site, together with an appreciable amount of water incorporated in the structure, with the consequent reduction of crystallinity.The information obtained in the present work suggests that (Ca,Zn)Hap doped with zinc below 6.2 wt % has a thermal stability over 800 °C which results in ceramic formed by a single phase of zinc-hydroxyapatite. It should be noted that, to our knowledge, the zinc-doped ceramic biomaterials obtained at the present time are a mixture of β-(Zn,Ca)3(PO4)2 and CaHap. Thus, the studies in this work allow obtaining a (Ca,Zn)Hap apatite stable above 800 °C that could potentially be used as a biomaterial useful in bone repair applications.

Search for new apatite-like phases for lead utilization based on crystal structure and thermal expansion

Apatites, being one of the most numerous mineral-like families of compounds, are considered as a matrix for binding lead ions, which is dangerous for the biosphere. The crystal-chemical (composition, structure) and thermophysical aspects (thermal expansion) are considered as the basis for analysing the properties of this kind of material. It is suggested that substances of the composition Pb5(AIVO4)2(BVIO4), Pb5(AIVO4)(CVO4)2 can be a perspective form of lead binding materials based on compounds with the structure of apatite (AIV = Si, Ge; BVI = S, Cr; CV = P). Such compounds, as it was shown by DTA and HTXRD experiments, are distinguished by the absence of polymerphism and the abnormal ordering of structure. Also, they have relatively low values of thermophysical indicators (the rate of change of linear thermal expansion coefficients is 0.02?0.03?106 K-1; values of the volume thermal expansion coefficients are 40?70?106 K-1). Compounds Pb5(SiO4)(PO4)2 (a = 9.78782(16) ?, c = 7.31084(16) ?, V = 606.555(23) ?3, R-bragg = 4.694 %) and Pb5(GeO4)(PO4)2 (a = 9.87697(12) ?, c = 7.33136(11) ?, V = 619.388(17) ?3, R-bragg = 1.730 %) were obtained, identified and crystallographically characterised for the first time.